Influence of binders on infrared laser ablation of powdered tungsten carbide pressed pellets in comparison with sintered tungsten carbide hardmetals studied by inductively coupled plasma atomic emission spectrometry

Laser ablation (LA) was studied as a sample introduction technique for the analysis of powdered and sintered tungsten carbides (WC/Co) by inductively coupled plasma optical emission spectrometry (ICP–OES). The possibility to work with powdered and compact materials with close chemical composition provided the opportunity to compare LA sampling of similar substances in different forms that require different preparation procedures. Powdered WC/Co precursors of sintered hardmetals were prepared for the ablation as pressed pellets with and without powdered silver as a binder, while sintered hardmetal blocks were embedded into a resin to obtain discs, which were then smoothed and polished. A Q-switched Nd:YAG laser operated at its fundamental wavelength of 1064 nm with a pulse frequency of 10 Hz and maximum pulse energy of 220 mJ was used. A single lens was used for the laser beam focusing. An ablation cell (14 cm³) mounted on a PC-controlled XY-translator was connected to an ICP spectrometer Jobin Yvon 170 Ultrace (laterally viewed ICP, mono- and polychromator) using a 1.5-m tubing (4 mm i.d.). Ablation was performed in a circular motion (2 mm diameter). Close attention was paid to the study of the crater parametres depending on hardness, cohesion and Ag binder presence in WC/Co samples. The influence of the Co content on the depth and structure of the ablation craters of the binderless pellets was also studied. Linear calibration plots of Nb, Ta and Ti were obtained for cemented WC/Co samples, binderless and binder-containing pellets. Relative widths of uncertainty intervals about the centroids vary between ± 3% and ± 7%, and exceptionally reach a value above 10%. The lowest determinable quantities (LDQ) of Nb, Ta and Ti calculated from the calibration lines were less than 0.5% (m/m). To evaluate the possibility of quantitative elemental analysis by LA–ICP–OES, two real sintered WC/Co samples and two real samples of powdered WC/Co materials were analysed. The results of LA–ICP–OES real sample analysis correlated well with the results obtained by X-ray fluorescence (sintered samples) and pneumatic nebulization inductively coupled plasma optimal emmission spectrometry (powdered samples) with a bias not exceeding 6.5%.     

Characterization of Cu-Sn/Pb diffusion zones of microelectronic contacts by means of electron probe microanalysis and ion beam sputtering

Physical parameters of material, such as strength and electrical conductivity, can be influenced considerably by the intermetallic compounds formed by diffusion in soldered microelectronic contacts between Cu and Sn/ Pb solders. Therefore, formation and growth of these contact zones were systematically investigated on model specimens in dependence on temperature, time and chemical tin-lead concentration of the solders by means of electron probe microanalytical investigations and characterized by phase growth constants. Compared with the conventional metallographic specimen preparation method, the ion beam etching of the contact surfaces proves to be an excellently suitable means for representing the microstructure after the cooling of the samples. Moreover, the three-dimensional grain structure and technologically caused defects in the contact can be shown by ion beam slope cutting. Effects as e.g. the dendritic growth and Kirkendall pores which increasingly occur at higher temperatures are successfully proved.     

Characterization of Cu-Sn/Pb diffusion zones of microelectronic contacts by means of electron probe microanalysis and ion beam sputtering

Physical parameters of material, such as strength and electrical conductivity, can be influenced considerably by the intermetallic compounds formed by diffusion in soldered microelectronic contacts between Cu and Sn/Pb solders. Therefore, formation and growth of these contact zones were systematically investigated on model specimens in dependence on temperature, time and chemical tin-lead concentration of the solders by means of electron probe microanalytical investigations and characterized by phase growth constants. Compared with the conventional metallographic specimen preparation method, the ion beam etching of the contact surfaces proves to be an excellently suitable means for representing the microstructure after the cooling of the samples. Moreover, the three-dimensional grain structure and technologically caused defects in the contact can be shown by ion beam slope cutting. Effects as e.g. the dendritic growth and Kirkendall pores which increasingly occur at higher temperatures are successfully proved.     

Preparation of VPS and PVD coatings for metallographic and TEM investigations

The aim of the first part of the paper is to give some advice for the faultless metallographic preparation of vacuum plasma sprayed coatings. Several coating/substrate combinations using metals, alloys and ceramics were investigated to derive some general rules. The second part deals with a preparation technique for cross-sections- of physical vapour deposition coatings. This technique was optimized for TiN and Ti(C, N) coatings on hardmetals which were examined in an analytical transmission electron microscope.     

Quantitative Mass Spectrometry of Decarburisation and Denitridation of Cemented Carbonitrides During Sintering

 Quantitative quadrupole mass spectrometry of (Ti, W)C-based cemented carbonitrides was carried out in order to monitor the evolution of the gas species as a function of time and temperature during vacuum sintering. Solid standards and gas mixtures as well as precise flow control were employed for calibration. Upon integration of the outgassing rates the carbon and nitrogen evolutions and mass losses during sintering of raw hardmetal powder mixtures (WC, TiC,…) and cemented carbonitrides could be quantified. Outgassing occurs in the range of temperatures 490–1480 °C. Nitrogen outgassing of (Ti, W)(C, N) was greater than that of Ti(C, N) due to the presence of W which increases the nitrogen activity in the solid causing a higher nitrogen equilibrium pressure. TiN showed a CO (0.2 wt%) and N₂ (0.5 wt%) weight loss only in the presence of the binder phase. For powder mixtures, it was observed that the amount of CO, CO₂ and N₂ liberated during vacuum sintering increased with the addition of cobalt in comparison with the same powders without binder phase. Nitrogen containing cermet alloys showed a greater loss of carbon than (Ti, W)C-based hardmetals. A careful control of carbon content by doping seems to be necessary in such alloys to avoid η-phase formation. Received July 7, 2000. Revision December 4, 2000.     

Direct solid analysis of powdered tungsten carbide hardmetal precursors by laser-induced argon spark ablation with inductively coupled plasma atomic emission spectrometry

The potential of the laser-induced argon spark atomizer (LINA-Spark atomizer) coupled with ICP-AES as a convenient device for direct analysis of WC/Co powdered precursors of sintered hardmetals was studied. The samples were presented for the ablation as pressed pellets prepared by mixing with powdered silver binder containing GeO₂ as internal standard. The pellets were ablated with the aid of a Q-switched Nd:YAG laser (1064 nm) focused 16 mm behind the target surface with a resulting estimated power density of 5 GW cm^–2. Laser ablation ICP-AES signals were studied as a function of ablation time, and the duration of time prior to measurement (pre-ablation time) which was necessary to obtain reliable results was about 40 s. Linear calibration plots were obtained up to 10% (m/m) Ti, 9% Ta and 3.5% Nb both without internal standardization and by using germanium as an added internal standard or tungsten as a contained internal standard. The relative uncertainty at the centroid of the calibration line was in the range from ±6% to ±11% for Nb, Ta and Ti both with and without internal standardisation by Ge. A higher spread of points about the regression was observed for cobalt for which the relative uncertainty at the centroid was in the range from ±9% to ±14%. Repeatability of results was improved by the use of both Ge and W internal standards. The lowest determinable quantities calculated for calibration plots were 0.060% Co, 0.010% Nb, 0.16% Ta and 0.030% Ti with internal standardization by Ge. The LA-ICP-AES analyses of real samples led to good agreement with the results obtained by solution-based ICP determination with a relative bias not exceeding 10%. The elimination of the dissolution procedure of powdered tungsten (Nb, Ta, Ti) carbide is the principal advantage of the developed LA-ICP-AES method.     

4种激光粒度仪对下蜀土湿法粒度测试的对比研究

使用4种应用较为广泛的激光粒度仪(Mastersizer2000、Bettersize2000、Horiba LA950和LS13320)对粒度差异较小的下蜀土(土塘剖面)进行了测试,从而对比分析不同激光粒度仪对于下蜀土的粒度组成测试差异及其这种差异对研究结果可能产生的影响.结果表明:对粉砂颗粒组分的分析,4种激光粒度分析仪分析结果的差异最小,而对砂和粘土颗粒组分分析的差异最大.就粒度频数曲线、概率累积曲线、粒度组分、C-M图、粒度参数散点图及粒度参数剖面垂向变化等统计参数与统计方式而言,4种仪器的测试结果均有一定的差异,其中,概率累积曲线、粒度参数散点图差异较大.粒度参数的剖面变化差异也较大,影响了对剖面的阶段性划分,这在一定程度上影响了研究结果,造成使用不同仪器,可能会得出不同的结果.     

Chemical analysis of the submicron binder phase in hard metals

Summary Chemical Analysis of the Submicron Binder Phase in Hard Metals The chemical analysis of the cobalt binder phase in sintered hard metals poses severe problems if performed by means of physical methods of surface analysis, such as SIMS, EMPA or AES. Compared with their limit of lateral resolution the average mean free path of the binder phase between the carbide particles, especially in micrograin hard metals, is less than 500 nm and thus too small. An electrochemical technique has been developed by which the carbide phase can be selectively etched away from the surface of a polished section, leaving the cobalt binder phase chemically and morphologically unchanged. The carbide-free cobalt binder phase can now be separated from the bulk hard metal using a technique similar to the well-known extraction replica technique commonly applied in transmission electron microscopy. The extracted binder phase can then be analyzed by X-ray fluorescence or other methods.     

Kinetics of isothermal oxidation of WC–20Co hot-pressed compacts in air

The present paper presents an isothermal analysis of the oxidation behavior in which hot-pressed compacts rather than powders are used over the temperature range 700–850 °C. This was done to better simulate the extent of oxidation occurring on use. WC–Co powders were first subjected to non-isothermal kinetic analysis to follow the oxidation mechanism. In the isothermal runs, a thermobalance was used to follow up the mass with time at different constant temperatures. The diameter of compacts was measured as function of time at these temperatures, and a simple model was proposed to relate the diameters to extent of oxidation. Two reactions were found to take place that are controlled by chemical reaction at interface: Oxidation of cobalt and oxidation of WC with the formation of WO₃ and CoWO₄. The activation energies for the two steps of oxidation were calculated and found to equal 157 kJ mol^?1 and 205 kJ mol^?1, respectively. These values are in reasonable agreement with published data for WC–Co powders.     

The influence of Ti plasma etching pre-treatment on mechanical properties of DLC film on cemented carbide

The pre-treatment of substrate surface had been a key part of DLC film preparation to improve mechanical and tribological properties. Ti plasma etching pre-treatment was investigated in this paper as a new effective surface pre-treatment method to substitute transition layer. This pre-treatment used high-energy Ti plasma to impact substrate surface. Ti plasma etched the substrate to a depth of 407 nm and increased the roughness from 1.36 to 40.39 nm. A trace layer of substrate, together with cobalt, oxides, and other impurities, was removed. Ti plasma broke some top WC crystals and combined with the free carbon ions separating from the substrate. A DLC film was deposited on the etched surface. Compared with DLC films deposited on the untreated substrate and Ti transition layer, the DLC film on the Ti plasma etched substrate had best adhesion strength of 34.14 N. The three DLC films had the same sp³ bonding carbon content, but Ti plasma etching treatment could promote the formation of sp³ bonds on the interface of substrate and DLC film. This DLC film had low friction coefficient of 0.12 and low wear rate of 5.11 × 10⁻⁷ mm³/m·N. In summary, Ti plasma etching pre-treatment could significantly improve the adhesion of DLC film and keep its excellent tribological properties.     

DLVO interactions of tungsten oxide and cobalt oxide surfaces measured with the colloidal probe technique

We have investigated the DLVO surface forces of oxidized tungsten and cobalt surfaces using the atomic force microscope (AFM) colloidal probe technique. It was shown by X-ray photoelectron spectroscopy (XPS) and electrokinetic measurements that this model system is representative of industrial tungsten carbide (WC) and cobalt powders used in the production of hard metals. We found that the attractive van der Waals forces are well described by Hamaker constants, calculated from optical data for WO(3) and CoOOH. The repulsive electrostatic double layer forces between WO(3) surfaces increase with increasing pH due to an increasingly negative surface potential. This surface potential decreases with increasing ionic strength at pH 7.5. The electrostatic interaction between WO(3) and CoOOH is attractive at pH 10, suggesting a positively charged CoOOH surface.     

Highly Active Cobalt‐Based Electrocatalysts with Facile Incorporation of Dopants for the Oxygen Evolution Reaction

In situ formation of electroactive cobalt species for the oxygen evolution reaction is simply achieved by applying an anodic bias to a commercially available cobalt precursor and Nafion binder mixture coated on a glassy carbon electrode. This preparation does not require energy‐intensive materials preparation steps or noble metals, yet a low overpotential of 322 mV at 10.2 mA cm^?2 and a high current density of more than 300 mA cm^?2 at 1.7 V_NHE were obtained in 1 m KOH. An operando electrochemical Raman spectroscopy study confirmed the formation of cobalt oxyhydroxide species and the iron stimulated the equilibrium state between Co³⁺ and Co⁴⁺. The iron present in the alkali electrolyte or ink solution effectively activated the cobalt species, and most of the first row transition metals could also enhance the catalytic performance. The concept presented here is one of the simplest strategies for preparing highly active electrocatalysts and is very flexible for the replacement of cobalt by other transition metals.     

Influence of the pore structure of MCM-41 and SBA-15 silica fibers on atomic layer chemical vapor deposition of cobalt carbonyl

Mesoporous high surface area MCM-41 and SBA-15 type silica materials with fibrous morphology were synthesized and used as support materials for the ALCVD (atomic layer chemical vapor deposition) preparation of Co/MCM-41 and Co/SBA-15 catalysts. Co/MCM-41 and Co/SBA-15 catalysts were prepared by deposition of Co2(CO)8 from the gas phase onto the surfaces of preheated support materials in a fluidized bed reactor. For both silica materials, two different kinds of preparation methods, direct deposition and a pulse deposition method, were used. Pure silica supports as well as supported cobalt catalysts were characterized by various spectroscopic (IR) and analytical (X-ray diffraction, Brunauer-Emmett-Teller, elemental analysis) methods. MCM-41 and SBA-15 fibers showed considerable ability to adsorb Co2(CO)8 from the gas phase. For MCM-41 and SBA-15 silicas, cobalt loadings of 13.7 and 12.1 wt % were obtained using the direct deposition method. The cobalt loadings increased to 23.0 and 20.7 wt % for MCM-41 and SBA-15 silicas, respectively, when the pulse deposition method was used. The reduction behavior of silica-supported cobalt catalysts was found to depend on the catalyst preparation method and on the mesoporous structure of the support material. Almost identical reduction properties of SBA-15-supported catalysts prepared by different deposition methods are explained by the structural properties of the mesoporous support and, in particular, by the chemical structure of the inner surfaces and walls of the mesopores. Pulse O2/H2 chemisorption experiments showed catalytically promising redox properties and surface stability of the prepared MCM-41- and SBA-15-supported cobalt catalysts.     

Chemical etching of zinc oxide for thin-film silicon solar cells

Chemical etching is widely applied to texture the surface of sputter-deposited zinc oxide for light scattering in thin-film silicon solar cells. Based on experimental findings from the literature and our own results we propose a model that explains the etching behavior of ZnO depending on the structural material properties and etching agent. All grain boundaries are prone to be etched to a certain threshold, that is defined by the deposition conditions and etching solution. Additionally, several approaches to modify the etching behavior through special preparation and etching steps are provided.     

Influence of grain orientation on zinc enrichment and surface morphology of an Al?Zn alloy

Zinc is an important alloying element in the 7000 series aluminium alloys. It is also an element that may enrich near the alloy surface during treatments of aluminium alloys by processes such as electropolishing, alkaline anodic etching and alkaline etching. The enrichment may occur since the change in Gibbs free energy per equivalent for formation of ZnO is less negative than that for formation of Al₂O₃. The enriched alloying element is present in an alloy layer up to ～5 nm thick located immediately beneath the alloy/film interface. In the present study, the dependence of the enrichment of zinc on the grain orientation of the alloy is investigated for a solid solution Al‐1.1at.%Zn alloy. The enrichment of the zinc is developed by alkaline etching of the alloy. The grain orientation is determined by electron backscattering diffraction, with enrichments quantified on selected grains by Rutherford backscattering spectroscopy and medium energy ion scattering. The morphologies of the surfaces of the etched grains are characterised by scanning electron microscopy and atomic force microscopy. The findings reveal that the zinc enrichment ranges from 1.7 × 10¹⁵ atoms/cm² to 3.9 × 10¹⁵ atoms/cm², with the greatest enrichment occurring on a grain of (100) orientation, while differing surface topographical textures are developed on the various grains. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and characterization of volatile liquid cobalt amidinates

Three new volatile cobalt amidinate compounds were prepared: Co(tBuNC(R)NEt)2, R=Me, Et and n-Bu. They were characterized by elemental analysis, 1H NMR, X-ray structure analysis, melting point, vapor pressure, vaporization rate, thermal stability and chemical reactivity. They were found to evaporate cleanly without decomposition. Two of them are liquids at room temperature, allowing for more convenient preparation, handling and purification by distillation. They are highly reactive compounds that have been found to be suitable precursors for vapor deposition of cobalt metal, cobalt nitride and cobalt oxide. A new synthetic method allows for the facile and inexpensive preparation of large quantities of these compounds.     

Optimization of permanganic etching of polyethylenes for scanning electron microscopy

The permanganic etching technique has been studied as a function of time, temperature, and concentration for a series of polyethylenes. Kinetic studies show that a film of reaction products builds up on the surface, impeding further etching, an effect which is greatest for the lowest-crystallinity polymers. SEM studies combined with EDS show that the film contains sulfur, potassium, and some manganese. An artifact is produced by the etching process which is impossible to remove by washing procedures if certain limits of time, temperature, and concentration are exceeded. For lower-crystallinity polyethylenes multiple etching and washing steps were required for optimal resolution. Plastic deformation during specimen preparation, whether from scratches or freeze fracturing, enhances artifact formation. When appropriate procedures are used virtually artifact-free surfaces can be produced allowing a combination of permanganic etching and scanning electron microscopy to give a rapid method for detailed morphological characterization of bulk specimens.     

Inert sampling and sample preparation - the influence of oxygen on heavy metal mobility in river sediments

Two approaches have been used to investigate changes in the nature of metal binding in river sediments caused by atmospheric oxygen. Firstly, non-inert and inert sample preparation were applied, in combination with sequential extraction, to determine for which metals inert sample preparation is necessary for correct determination of metal mobility under environmental conditions. Secondly, the metal contents of sediments sampled before and after a river weir were fractionated by sequential extraction to study the effect of the oxygen impact at the weir on heavy metal mobility in the sediments. Different grain-size fractions from one sample were also extracted, to enable selection of the upper grain-size limit most suitable for answering this analytical question. The results showed the need for the inert sample preparation technique for Cd, Zn, Pb, Mn, and Fe, but not for Co, Ni, Cu, and Cr. No significant change of heavy metal mobility at the weir could be proved, although the mobilization behavior of some elements was different. The optimum upper grain-size limit was 63 microm.     

Preparation and characterisation of hydroxide stabilised ZnO(0001)-Zn-OH surfaces

Two different approaches under ambient conditions were developed for the preparation of clean, non-reconstructed, single crystalline ZnO(0001)-Zn surfaces. The surface preparation by a wet chemical etching procedure was compared with the same treatment in combination with a subsequent heat treatment in humidified oxygen atmosphere. Depending on the preparation technique, atomically flat terraces with a width of 100 nm to several micrometers were observed using an atomic force microscope (AFM). The obtained surface structures were further characterized by means of angle resolved X-ray photoelectron spectroscopy (AR-XPS), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), Auger electron spectroscopy (AES) and low energy electron diffraction (LEED) measurements. Based on these results it is shown that the obtained surfaces are, in contrast to surfaces prepared under UHV conditions, stabilised by the adsorption of a monolayer of hydroxides. The important role of H(2)O during the heat treatment is pointed out by comparing the results of the same heat treatment in the absence of water. H(2)O turned out to play an important role in the reorganization process of the surface at elevated temperatures, thereby yielding extremely large atomically flat terraces. The terminating edges of these terraces were found to include 120 degrees and 60 degrees angles, thus perfectly reflecting the hexagonal surface structure.     

Influence of the grain size on the quality of standardless WDXRF analysis of river Nile sediments

In multichannel wavelength-dispersive X-ray fluorescence spectrometry (WDXRF) the fluorescence intensity might depend on grain size and heterogeneity of the sample. Six river Nile sediment samples were collected two meters below the water surface from different locations covering the greater Cairo, Egypt. Each sample was dried at 65 °C for 48 h and divided into four grain size fractions: < 32 μm, 32–63 μm, 63–125 μm and 125–200 μm using different sieves. The dry sediment samples were mixed with low contamination binder (Wax, C₆H₈O₃N₂) in a mass ratio of wax:sample = 4:0.9 g. Sample pellets were made using a hydraulic press at a pelletizing pressure of 120 KN cm^{− 2}. The results show that the XRF intensities of the K_α radiation might increase or decrease with decreasing grain size, depending on the atomic number of the analyte. In the present thick pelletized samples, the penetration depth of the characteristic radiation increases at low grain sizes, and consequently the probability of the grain-size effect on the characteristic radiation decreases. Depending on the experimental data, a general theoretical equation, relating fluorescence intensity, grain size and atomic number, was derived by using cubic spline interpolation. The fractions were identified by WDXRF using standardless quantitative analysis, depending on the fundamental parameter approach. According to the present statistical analysis and the Certified Reference Material (CRM) results, the quantitative analysis results were found acceptable when the grain size of the river Nile sediments less than 32 μm. At a grain size > 63 μm, standardless analysis using fundamental parameter approach was found to be useful for qualitative and semi-quantitative analysis only whereas there are a strong positive correlations.