Some topical applications of plasma atomic spectrochemical methods for the analysis of ceramic powders

The scope of a number of plasma spectrochemical methods for the determination of the main components and impurities in ceramic powders is described. These methods meet the requirements for the analytical characterization of new structural and functional ceramics for modern industrial applications and electronic devices. For ceramic powders, spectrochemical analysis with direct methods as well as analysis subsequent to sample dissolution are discussed. Fusion is a powerful method for the dissolution of ZrO₂ ceramic powders, provided the fluxes are pure enough. For determinations in Al₂O₃, SiC and ZrO₂, it will be shown that ICP-MS is very useful. This is especially true for trace analysis after matrix removal. The latter can easily be performed on-line in the case of the analysis of Al₂O₃ powders. For direct analysis of ceramic powders, the direct insertion of samples into the plasma, spark and arc ablation, laser ablation, electrothermal vaporization and slurry nebulization are discussed. Particular attention is given to the direct analysis of ceramics in powder form (Al₂O₃, SiC, Si₃N₄, B₄, WC) using ICP-OES with slurry nebulization as well as with direct sample insertion (DSI) and with electrothermal vaporization (ETV). For the two latter methods, the use of chemical modifiers for volatile compound formation will be shown to be of great importance, and its features will be explained using thermochemical considerations.     

Some topical applications of plasma atomic spectrochemical methods for the analysis of ceramic powders

The scope of a number of plasma spectrochemical methods for the determination of the main components and impurities in ceramic powders is described. These methods meet the requirements for the analytical characterization of new structural and functional ceramics for modern industrial applications and electronic devices. For ceramic powders, spectrochemical analysis with direct methods as well as analysis subsequent to sample dissolution are discussed. Fusion is a powerful method for the dissolution of ZrO₂ ceramic powders, provided the fluxes are pure enough. For determinations in Al₂O₃, SiC and ZrO₂, it will be shown that ICP-MS is very useful. This is especially true for trace analysis after matrix removal. The latter can easily be performed on-line in the case of the analysis of Al₂O₃ powders. For direct analysis of ceramic powders, the direct insertion of samples into the plasma, spark and arc ablation, laser ablation, electrothermal vaporization and slurry nebulization are discussed. Particular attention is given to the direct analysis of ceramics in powder form (Al₂O₃, SiC, Si₃N₄, B₄, WC) using ICP-OES with slurry nebulization as well as with direct sample insertion (DSI) and with electrothermal vaporization (ETV). For the two latter methods, the use of chemical modifiers for volatile compound formation will be shown to be of great importance, and its features will be explained using thermochemical considerations. Received: 18 February 1998 / Revised: 13 May 1998 / Accepted: 9 June 1998     

Multielement trace determination in SiC powders: assessment of interlaboratory comparisons aimed at the validation and standardization of analytical procedures with direct solid sampling based on ETV ICP OES and DC arc OES

The members of the committee NMP 264 “Chemical analysis of non-oxidic raw and basic materials” of the German Standards Institute (DIN) have organized two interlaboratory comparisons for multielement determination of trace elements in silicon carbide (SiC) powders via direct solid sampling methods. One of the interlaboratory comparisons was based on the application of inductively coupled plasma optical emission spectrometry with electrothermal vaporization (ETV ICP OES), and the other on the application of optical emission spectrometry with direct current arc (DC arc OES). The interlaboratory comparisons were organized and performed in the framework of the development of two standards related to “the determination of mass fractions of metallic impurities in powders and grain sizes of ceramic raw and basic materials” by both methods. SiC powders were used as typical examples of this category of material. The aim of the interlaboratory comparisons was to determine the repeatability and reproducibility of both analytical methods to be standardized. This was an important contribution to the practical applicability of both draft standards. Eight laboratories participated in the interlaboratory comparison with ETV ICP OES and nine in the interlaboratory comparison with DC arc OES. Ten analytes were investigated by ETV ICP OES and eleven by DC arc OES. Six different SiC powders were used for the calibration. The mass fractions of their relevant trace elements were determined after wet chemical digestion. All participants followed the analytical requirements described in the draft standards. In the calculation process, three of the calibration materials were used successively as analytical samples. This was managed in the following manner: the material that had just been used as the analytical sample was excluded from the calibration, so the five other materials were used to establish the calibration plot. The results from the interlaboratory comparisons were summarized and used to determine the repeatability and the reproducibility (expressed as standard deviations) of both methods. The calculation was carried out according to the related standard. The results are specified and discussed in this paper, as are the optimized analytical conditions determined and used by the authors of this paper. For both methods, the repeatability relative standard deviations were <25%, usually ~10%, and the reproducibility relative standard deviations were <35%, usually ~15%. These results were regarded as satifactory for both methods intended for rapid analysis of materials for which decomposition is difficult and time-consuming. Also described are some results from an interlaboratory comparison used to certify one of the materials that had been previously used for validation in both interlaboratory comparisons. Thirty laboratories (from eight countries) participated in this interlaboratory comparison for certification. As examples, accepted results are shown from laboratories that used ETV ICP OES or DC arc OES and had performed calibrations by using solutions or oxides, respectively. The certified mass fractions of the certified reference materials were also compared with the mass fractions determined in the interlaboratory comparisons performed within the framework of method standardization. Good agreement was found for most of the analytes.     

无压烧结合成高纯度Ti3SiC2粉体

本文通过优化混合方式将Ti、Si、石墨和Al等粉末按照一定配比混合后,在1 420℃氩气保护下合成了Ti3SiC2粉末。用XRD和SEM分别分析了样品中的相成分、微观形貌,计算得出其质量百分含量,高达96.7%,研究了烧结工艺中降温速率对Ti3SiC2微观形貌的影响,并讨论了其生长机理。本工艺原料混合简单有效,得到的产品纯度高,因而有助于实现Ti3SiC2粉末的批量生产。     

Direct multielement trace analyses of silicon carbide powders by spark ablation simultaneous inductively coupled plasma optical emission spectrometry

A procedure for the direct analysis of silicon carbide powders (SiC) by simultaneous detection inductively coupled plasma optical emission spectrometry using a Spectro-CIROS™ spectrometer (CCD-ICP-OES) and a novel spark ablation system Spectro-SASSy (SA) as sample introduction technique is described. The sample preparation procedure for SA of non-conducting material is based on mixing the sample powders with a conducting matrix, in this case copper and briquetting pellets. Pressing time, pressure and mixing ratio are shown to be important parameters of the pelleting technique with respect to their mechanical stability for the reliability of the analysis results. A mixing ratio of 0.2 g +0.6 g for SiC and Cu, a pressure of 10 t cm^− 2 and a pressing time of 8 min have been found optimum. It has also been shown that the spark parameters selected are crucial for uniform volatilization. Electron probe micrographs of the burning spots and the analytical signal magnitude showed that a rather hard spark at 100 Hz was optimum. The determination of trace elements in silicon carbide powders is demonstrated using a calibration based on the addition of standard solutions. For Al, Ti, V, Mn and Fe detection limits in the lower µg g^− 1 range can be achieved. Internal standardization with Y in combination with the addition of standard solutions allows relative standard deviations in the range of 4 to 24% for concentration levels of the order of 3 to 350 µg g^− 1.     

Advanced ceramics and their basic products: A challenge to the analytical sciences

The analytical characterization required in the development and in the quality control of new ceramics is discussed. For the basic substances, the problems encountered in the development of routine techniques for a direct and reliable analysis of Al₂O₃, AlN, Si₃N₄, SiC, and ZrO₂ powders are reported. Among the atomic spectrometric methods, especially slurry atomization ICP-spectrometry is described. Also the problems encountered in the development of combined procedures as required for the characterization of reference samples are presented. Methods for the direct bulk analysis of ceramics and microdistributional analysis, as they are now under development with laser-based techniques and various probe techniques, are described as well.     

Modelling of the evaporation behaviour of particulate material for slurry nebulization inductively coupled plasma atomic emission spectrometry

This paper is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta, Part B (SAB). This hardcopy text, comprising the main body and an appendix, is accompanied by a disk with programs, data files and a brief manual. The main body discusses purpose, design principle and usage of the computer software for modelling the evaporation behaviour of particles in inductively coupled plasma atomic emission spectrometry (ICP-AES). Computer software has been developed in FORTRAN 77 language in order to simulate the evaporation behaviour of particles of refractory materials such as encountered in the analysis of advanced ceramic powders by slurry nebulization inductively coupled argon plasma atomic spectrometry. The program simulates the evaporation of single particles in the inductively coupled plasma and also enable it to calculate on the base of a given particle size distribution the evaporation behaviour of all the particles contained in a sample. In a so-called “intensity concept”, the intensity is calculated as a function of the observation height in order to determine recovery rates for slurries compared with aqueous solutions. This yields a quick insight whether a calibration with aqueous solutions can be used for analysis of slurries of a given powder by slurry nebulization ICP-AES and also is a help in determining the optimal parameters for analyses of powders by means of slurry nebulization ICP-AES.Applications for the evaporation of Al₂O₃ and SiC powders document the usefulness of the model for the case of a 1.5 kW argon ICP of which the temperature at 8 mm above the load coil has been determined to be 6100 K. The model predicts the maximum particle size for SiC and Al₂O₃ that can be transported (10–15 μm) and evaporated for a given efficiency under given experimental conditions. For both Al₂O₃ and SiC, two ceramic powders of different grain size were investigated. The median particle sizes cover the range typical of ceramic powders. Investigations were made for SiC A 10 (median particle size 2.2 μm), SiC F1200 (4.3 μm) and Al₂O₃ AKP 30 (< 1.9 μm) and Al₂O₃ Cilas 715 (3.0 μm), respectively, in which particles with diameters of up to 23 μm still are found.     

Emanation Thermal Analysis of SiC Based Materials

Results of emanation thermal analysis (ETA) characterizing microstructure changes of SiC based materials during heat treatment in argon are demonstrated. This method made it possible to reveal fine changes of the texture of SiC nano-sized powders, SiC micro-sized powders and SiC whiskers under in situconditions of the heating. ETA curves can serve as fingerprints of the respective samples.This revised version was published online in November 2005 with corrections to the Cover Date.     

The use of plasma atomic spectrometric methods for the analysis of ceramic powders

The use of plasma atomic spectrometric methods for the analysis of high-purity refractory powders of Al₂O₃, SiC and ZrO₂ used in the production of advanced ceramics is discussed. Special reference is given to the use of combined procedures including sample decomposition and in the case of ZrO₂ to matrix removal as well as to the slurry technique as a direct method in atomic spectrometry with inductively coupled plasmas (ICP). Both the possibilities, limitations and analytical use of the slurry technique are discussed and shown to be related to the particle size of the powder; this should be below the 5–10 m level. The use of a Simplex method for the optimization of the slurry technique towards obtaining both the highest power of detection and calibration using solutions will be treated for the case of SiC. A critical evaluation of the use of ICP atomic emission and of ICP mass spectrometry is presented.     

Rheological Properties of SiC Suspensions with a Compound Surface Modification Using Ethyl Orthosilicate and Ethylene Glycol

Ultrafine silicon carbide (SiC) powders were surface-modified using ethyl orthosilicate (TEOS) combined with ethylene glycol. SiC suspensions with favorable rheological properties, low viscosity, and high solid loading were successfully obtained. The mechanisms of the compound surface modification for SiC powders as well as the influences of the compound surface modification not only on functional groups and charge state of the surface for SiC powders but also on the rheological properties of SiC suspensions were investigated in the present study. The results show that under alkaline conditions and acidic conditions, the surface charge states of SiC powders were [Si-OCH₂CH₂O]^? and [Si-OCH₂CH₂OH₂]⁺, respectively. The absolute value of zeta potential reached the maximum value of 22.69 mV at pH 11. Additionally, with added 1 wt% TEOS and 3 wt% ethylene glycol, the SiC suspensions exhibited good rheological properties, low viscosity and high stability due to the steric hindrance and electrostatic repulsion offered by the [Si-OCH₂CH₂O]^- with a high concentration.     

Preparation of MB<Subscript>2</Subscript>/SiC and MB<Subscript>2</Subscript>/SiC-MC (M = Zr or Hf) powder composites which are promising materials for design of ultra-high-temperature ceramics

This survey shows the prospects of studies targeted at preparing MB₂/SiC and MB₂/SiC-MC (M = Zr or Hf) nanosized composite powders for use in the manufacture of ultra-high-temperature ceramics (UHTCs) and antioxidant protective coatings on C_f/C and C_f/SiC composites. The survey considers the specifics of various preparation methods, including sol-gel technology or precipitation followed by borothermic/ carbothermic reduction, self-propagating high-temperature synthesis (SHS), specifically variants combined with mechanochemical activation or spark plasma sintering (SPS), chemical modification of ZrB₂(HfB₂) powders with polycarbosilane followed by pyrolysis, and dispersion of appropriate ceramics with the stabilization of the slurry. The elemental and phase compositions, particle sizes, microstructures, and some other characteristics of the products reported in the related literature are summarized.     

粉末压饼LA-ICP-MS测定土壤样品中微量元素

研究了采用粉末压饼制样LA-ICP-MS测定土壤样品中多元素的分析方法.在土壤样品中事先加入已知含量的In,并以聚四氟乙烯(PTFE)为粘合剂,在200 KN的压力下制备用于激光剥蚀的压饼.详细讨论了粉末压饼样品中元素的均一性及元素相对信号响应.所建立的方法用于土壤标准参考物质固体样品的直接分析,测定值与参考值具有较好的一致性.     

A comparison between photon counting histogram and fluorescence intensity distribution analysis

Photon counting histogram (PCH) and fluorescence intensity distribution analysis (FIDA) are two methods that were developed independently but reported almost simultaneously. Both of them have been successfully applied to fluorescence fluctuation spectroscopy (FFS). Though publications have indicated that they are theoretically equivalent, they are still commonly considered as different methods, especially in their ways to treat the point spread functions (PSFs). In this paper, the two methods are examined in detail for a direct comparison. After a direct proof of the theoretical equivalence, the authors further point out that PCH and FIDA are completely equivalent in the way of modeling PSFs; that is, any modeling approach developed from one of them can always be applied to the other. It is also demonstrated that simplified FIDA and PCH formulas in the form of power series can be applied for fast and precise numerical calculations. The two methods are also compared for their merits in the calculation efficiency.     

Analysis of silicon carbide powders with ICP-MS subsequent to sample dissolution without and with matrix removal

ICP-MS has been employed for the analysis of silicon carbide powders in connection with high pressure acid decomposition without and with matrix removal by evaporation. The powder is decomposed by treatment of a 250 mg sample with a mixture of HNO₃, H₂SO₄ and HF. Prior to the analyses with ICP-MS the solutions have to be diluted to a matrix concentration of 500 g/ml related to SiC in order to realize full long-term precision. The results obtained for Li, B, Na, Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Ni, Co, Cu, Zn, Ga, Sr, Y, Zr, Nb, Ag, Cd, In, Sn, Sb, Ba, La, Ce, Pr, Nd, Hf, Ta, W, Tl, Pb, Bi, Th and U in SiC powder S-933 are shown to be in good agreement with those of independent methods, such as INAA, ICP-AES with slurry atomization and ICP-AES subsequent to sample decomposition. For extending the use of ICP-MS to elements such as Mg, Ca, Sc and Ti at the relevant concentrations in SiC powders, a more effective matrix removal by evaporation of the decomposition solution to near dryness has been successfully applied. Its advantages have been proven by the results of high resolution ICP-MS. It has been found by analyses of the treated sample solutions for the residual Si and C with ICP-MS that over 99% of the matrix and also of the acids used for decomposition are removed. For B, Al and Fe losses were found to occur at concentration levels of some g/g, 200 g/g and 300 g/g, respectively, and all other elements were detected with very good recoveries. For all 36 elements investigated in this work the detection limits could be improved from the ng/g to the pg/g range by removal of the matrix. The analytical range could be improved, in particular for In, Tl, Bi and U.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

Analysis of advanced ceramics and their basic products

Summary A review on the analysis of the most important ceramic materials and their basic substances is given. The importance of minor and trace elements in the bulk as well as their distribution on the microscale in both classes of substances is discussed by the example of Al₂O₃, AlN, TiO₂, Si₃N₄, SiO₂, SiC, Y₂O₃, ZrO₂-based and some other ceramics and of their basic substances. The state-of-the-art and trends of development in modern atomic spectrometric methods for bulk analysis of the basic substances subsequent to sample dissolution, such as plasma emission and mass spectrometry, but also of direct methods such as slurry nebulization for plasma spectrometry, inorganic mass spectrometry and X-ray spectrometry are discussed. Further, first approaches for the in-depth analysis of powders and trends in direct methods for compact ceramics based on laser evaporation as well as on electron and ion probe techniques are presented. The latter are illustrated with selected examples from the literature.

---

Analyse von modernen keramischen Materialien und ihren Grundstoffen

---

Dedicated to Prof. Dr. R. Neeb on the occasion of his 60th birthday     

超细氮碳化物中吸附氧和化合氧的测定

用跟踪式程序升温、红外检测和微机解卷技术，测定氮碳化物超细粉的吸附氧和化合氧，探讨了超细Ｓｉ３Ｎ４，ＡＩＮ，ＴｉＣＮ和ＳｉＣ中不同状态氧量与其制备方法，颗粒度及放置时间的关系。     

Controlled Synthesis of β-SiC Nanopowders with Variable Stoichiometry Using Inductively Coupled Plasma

In the growing field of nanomaterials, SiC nanoparticles arouse interest for numerous applications. The inductively coupled plasma (ICP) technique allows obtaining large amount of SiC nanopowders from cheap coarse SiC powders. In this paper, the effects on the SiC structure of the process pressure, the plasma gas composition, and the precursor nature are addressed. The powders were characterized by X-ray diffraction (XRD), Raman and fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and high resolution electron microscopy (HREM), chemical analyses, BET and photon correlation spectroscopy (PCS) measurements. Whatever the precursor (α- or β-SiC), the nanoparticles were crystallised in the cubic β-SiC phase, with average sizes in the 20–40 nm range. Few residual grains of precursor were observed, and the decarburization due to the reductive Ar–H₂ plasma lead to the appearance of Si nanograins. The stoichiometry of the final product was found to be controllable by the process pressure and the addition of methane.     

Analysis of high purity graphite and silicon carbide by direct solid sampling electrothermal atomic absorption spectrometry

Solid sampling electrothermal atomic absorption spectrometry using the boat technique and a transversely heated graphite tube was applied to direct analysis of graphite and silicon carbide powders for 14 and 12 impurity elements, respectively. With graphite, for all analytes under investigation, a very effective in-situ analyte/matrix separation was achieved. That was the case also for analytes in silicon carbide requiring atomization temperatures below 2400 degrees C. At higher atomization temperatures, the decomposition products of silicon carbide give rise to significant background, which can still be corrected. Sample amounts of up to 4 mg graphite and 8 mg silicon carbide per analysis cycle were applied. For all analytes in both materials, limits of detection at the lower ng g(-1) and sub-ng g(-1) level were achieved, excluding arsenic for which they were 50 ng g(-1) and 23 ng g(-1) for graphite and silicon carbide, respectively. Quantification was performed using calibration curves measured with aqueous standard solutions. The accuracy was checked by comparison of the results with those obtained by instrumental neutron activation analysis and by other independent methods.     

Influence des conditions experimentales du depot de SiC par RCVD sur l'infiltration de substrats de carbone poreux

The infiltration by SiC of porous substrates of carbon or graphite powders by reaction between the substrate and an SiCl₄-H₂ gaseous mixture has been studied by the reactive chemical vapor deposition (RCVD) method as a function of temperature gaseous mixture composition and total flow rate. β-SiC has been characterised using ESCA spectroscopy, X-ray diffraction and chemical analysis with MASE spectroscopy. The silicon carbide is present throughout the sample. The growth rate of the SiC layer is very slow and the activation energy of the process is evaluated at 168 kJ mol⁻¹. High temperatures (1430 °C) and flow rates (950 cm³ min⁻¹) promote the deposition on the surface of the sample and the correct orientation of the crystals. The presence of whiskers has also been detected in the pores of the substrates.     

Determination of impurities in silicon carbide powders

Summary The analysis of SiC powders used for the production of high-performance ceramics was investigated by combined procedures as well as by a direct technique including atomic spectrometric detection. For the combined chemical procedure, SiC powders (0.25 g) were completely dissolved in a mixture of HNO₃, HF and fuming H₂SO₄ in an autoclave at 240°C within 8 to 20 h. In the final 0.5% w/v solution 13 elements were determined by electrothermal atomic absorption spectrometry (ETAAS) and by inductively coupled plasma atomic emission spectrometry (ICP-AES). With acid decomposition the detection limits for Ca, Cd, Cr, Cu, Mg, Mn and Zn were found to be in the range of 0.1–1 g/g; those for Al, B, Fe, Ni, Ti and V are at the 1–5 g/g level. With a Babingtontype nebulizer 1% slurries of SiC can be directly analyzed by ICP-AES. Calibration was performed by standard addition of aqueous solutions of the elements to be determined and the detection limits are close to those of ETAAS subsequent to pressure decomposition. The required analysis time was reduced from approx. 24 h to 30 min. First results for Ca, Cr, Cu, Mg, Mn, Ti and V as well as the needs to overcome systematic errors of this method, e.g. for Fe, are communicated.Part of this paper was presented at XI. International Symposium of Microtechniques, Wiesbaden, FRG, Aug. 28th–Sept. 1st 1989