Total Impurity Content Research Articles

Purification of cadmium up to 5N+ by vacuum distillation

Cadmium was refined by vacuum distillation, a technique suitable for low boiling and melting point materials, to remove the heavy and low vapour pressure impurities at ppm level. The detailed analysis of the purified Cd as well as raw Cd was done by ICP-OES techniques for 27 impurity elements. Purification was carried out in an efficient high-yield vacuum distillation system designed and fabricated for purifying 3N+ purity indigenous cadmium to 5N+ (99.999%). Analysis confirmed the reduction of total impurity content from 134 ppm (3N7) for raw Cd to 3 ppm (5N7) upon vacuum distilled Cd. The present study shows that the analysis of impurities such as Fe, Mg and Ca are contributed from environmental effect, whereas impurities such as Pb, Bi, Ag, Ni, Cu, Zn and Tl require adaptation of elemental analysing technique to counter dilution effect. The Hg trace analysis can however be carried out by hydride generation techniques.

The growth, morphology and perfection of fluoranthene crystals grown from supercooled chlorine derivative solutions on spontaneously formed seeds

Crystals of the aromatic hydrocarbon fluoranthene have been grown from supercooled solutions, employing five chlorinated hydrocarbons as solvents, on spontaneously formed seeds under conditions of constant temperature growth. Total impurity content in the material used for growth determined by GC-FID and GC-MS methods was ⩽10 −3 mass%. All the crystals grown possessed only columnar habit exhibiting simultaneously significant differences in the growth forms, mainly according to the solvent. The largest crystals of 50×12×5 mm 3 dimensions, exhibiting six forms, were grown from the nearest to ideal solution in trichloroethylene. Based on the measured solubility data, the activity coefficient and the dissolution enthalpy of fluoranthene were evaluated at the growth temperature of the crystals and used to interpret an observed solvent effect on their morphology and structural quality. Finally, the perfection of the crystals was examined using X-ray topography and the main growth-induced defects were identified as inclusions.

Electrical and thermal conductivities of Fe–Ni–Si alloy under core conditions

Extrapolation to core conditions of laboratory observations of electrical resistivities of iron and its alloys has been hampered by lack of understanding of interactions between the effects of temperature, pressure and impurities. We present a new theory that offers a simple resolution of the combined temperature and pressure effects: for a pure metal they can be represented by constant resistivity on the melting curve. On this basis the resistivity of pure iron under conditions in the outermost part of the core would be 1.22 μ Ω m. This reduces the estimation of core resistivity to an assessment of the impurity effect. Measurements by P.W. Bridgman on a range of iron alloys up to 10 GPa show that, for dilute alloys, impurity resistivity is proportional to total impurity content but relatively insensitive to which elements are present. Therefore, we use measurements by G. Matassov on Fe–Si alloys shock-compressed to 140 GPa to estimate the impurity contribution to core resistivity. Comparison with similar data for Fe and Fe–Ni alloy shows that under these conditions the effect of Si is only twice that of Ni on an atomic percent basis (and precisely the same on a weight percent basis). We estimate the total core resistivity to be about 2.1 μ Ω m with little variation in the outer core and 1.6 μ Ω m in the inner core. Allowing for a lattice thermal conductivity of 3 W m −1 K −1 the corresponding thermal conductivities are 46 W m −1 K −1 at the CMB, 63 W m −1 K −1 just above the ICB and 79 W m −1 K −1 in the inner core.

Preparation of High-Purity ZrF4and HfF4for Optical Fibers and Radiation-Resistant Glasses

The separation coefficients of ZrF4(HfF4) and metal fluoride impurities in the process of vacuum sublimation between 900 and 1200 K in the molecular vaporization regime were calculated. The separation coefficients were found to decrease in the order CrF2> MnF2> NiF2> CoF2> MnF3> FeF2> AlF3> CrF3> CuF2> FeF3 . The conditions for purification of ZrF4and HfF4by vacuum sublimation were optimized. The total impurity content in both fluorides was found to increase with the product of the evaporation rate per unit area and the degree of evaporation. Fe was found to be the most difficult-to-remove impurity in ZrF4and HfF4 . The production rate of the sublimating plant is about 100 kg/year of ZrF4and HfF4sublimates. ZrF4was used to prepare optical fibers for laser applications and noncontact fiber sensors for monitoring the composition and temperature of liquid radioactive waste. Fluorohafnate glasses were used to fabricate radiation-resistant scintillating modules of dimensions 20 × 30 × 150 mm, weighing ≤0.5 kg.

Impurities and evaluation of induced activity of CVI SiC f/SiC composites

Impurity of SiC f/SiC composites prepared by CVI was analyzed by neutron activation analysis and glow discharge mass spectrometry. The evaluation of the induced activity of the composites based on the chemical compositions was made using a simulation calculation for fusion reactor blanket. Impurities of 35 elements were detected in the composites. However, the total concentration of metallic impurities was below 20 mass ppm. The analyses of induced activity of the composites show that the dose rate decreases by about six orders of magnitude in a day after the shutdown. It is recommended that the purification of SiC composites, especially reduction of Fe and Ni contents, is necessary to reduce the activity to satisfy the limit of remote handling recycling after several 10 years cooling of fusion reactors.

Characterisation of undoped gallium antimonide grown by metalorganic chemical vapour deposition

Metalorganic chemical vapour deposition grown GaSb films on GaAs have been optimised for combined morphology, electrical and optical properties by variations in substrate temperature and V/III ratio. The transport properties of the films grown at 540°C depend on precursor ratios with a V/III ratio of 0.72 providing hole mobilities of around 500cm2V−1s−1 and hole concentration about 3×1016cm−3. For higher temperatures, the mobility decreases and the carrier concentration increases. Changing the V/III ratio for 540°C growth results in slight mobility loss in Sb-rich conditions and severe degradation in excess Ga conditions. Comparison of experimental and theoretical temperature dependencies of mobility shows good agreement, while differences between measured hole and inferred total impurity concentrations suggest the contribution of deeper compensating impurities. Films grown at lower temperatures were found to have very good optical quality and bandgaps equal to the bulk value of of 0.72eV. Above 500°C, the band tailing starts to develop, when substantial disorder becomes apparent at 560°C and above. This disorder is also observed in the Raman spectra of films grown at these temperatures. For the V/III ratio the highest optical quality was obtained for films grown with V/III=2.0. The excitonic features in absorption are observed for the first time in GaSb.

Growth of LiNbO 3 co-doped with Er 3+/Yb 3+

Single crystals of LiNbO 3 co-doped with Er 3+ and Yb 3+ have been grown by the Czochralski technique, from melts having a fixed erbium concentration (0.5 mol%) and different ytterbium concentrations (0.1, 0.5, 1.0, 1.5 and 2.0 mol%). Optical absorption measurements indicate the efficient incorporation of the rare-earth ions to the crystal, with the absorption bands characteristic of the 3 + valence. The co-doping with Yb 3+ increases substantially the absorption band in the 880–1040 nm region compared to Er-doped crystals. The incorporation of the rare-earth ions to the crystal is better described by considering both dopants as a single species with a solubility dependent on the total impurity concentration.

Quantitative Evaluation of Glass‐Forming Impurities in Alumina: Equivalent Silica Concentration (ESC)

Equivalent silica concentration (ESC) is proposed as a quantitative measure of the total impurity concentration that contributes to intergranular glass formation in nominally pure alumina. The method involves, in its determination, the processing and sintering of the alumina under contamination‐free conditions, as well as measuremet of the average grain size at the moment that abnormal grains first appear. This latter value can be converted to an ESC value from the inverse relationship between grain size and silica concentration, which can be established via an identical method using ultrapure alumina. The ESC values for four different commercial alumina powders of varying purity have been measured and compared with their chemical‐analysis data.

Analysis of the oxygen impurity atoms beneath the surface of Cz-silicon by CPAA

Charged particle activation analysis (CPAA) is able to analyze light elements such as carbon, nitrogen and oxygen at trace levels in materials. By comparison with other techniques such as Fourier transform infrared spectroscopy (FTIR), the major advantage of the CPAA is its ability to determine the total concentration of impurities (interstitial, substitutional or incorporated in a complex). Errors due to matrix effects and surface contamination are eliminated. However, this technique does not allow analysis in the first micrometers beneath the surface because the chemical etching, required to rid the surface of superficial contaminants, removes this important part of the compounds’ active zone. The aim of this study is to solve this problem and as a result to be able to determine impurities in the vicinity of the surface. An application on oxygen diffusion profiles in Cz-silicon submitted to a rapid thermal annealing (RTA) will be discussed.

Isolation and identification of process impurities in trimethoprim drug substance by high-performance liquid chromatography, atmospheric pressure chemical ionization liquid chromatography/mass spectrometry and nuclear magnetic resonance spectroscopy

Twenty-two lots of recently synthesized trimethoprim drug substance, from five different manufacturers, in three different countries of origin, China, Israel and the United States, were investigated for the presence of impurities. A liquid chromatographic system, using gradient elution, and a mobile phase consisting of 0.25% TEA/0.1% formic acid (pH 5.8)–acetonitrile, was used to separate and detect two significant, recurring impurities in trimethoprim drug substance. The two impurities were isolated by preparative liquid chromatography and identified, using a combination of liquid chromatography/mass spectroscopy and nuclear magnetic resonance, as 2,4-diamino-5-(4-ethoxy-3,5-dimethoxybenzyl) pyrimidine and 2,4-diamino-5-(3-bromo-4,5-dimethoxybenzyl) pyrimidine. These impurities were not detected by the compendial method and were present at significant levels in 17 of the lots tested. Total impurity concentrations were in the range of 0.1–2.1%.

Dynamic nuclear polarization of diamond. I. Solid state and thermal mixing effects

The dynamic nuclear polarization of 13C nuclei in a suite of seven natural type Ia and Ib diamonds, using continuous wave S- and X-band microwave radiation, is described. The 13C signal enhancement and polarization time have been measured for one of the type Ib diamonds as a function of magnetic field in the vicinity of the resonance field. The total paramagnetic impurity concentration (P1 and other centers) in this diamond is 2×1018 cm−3 (23 atomic parts per million), while the concentration of P1 centers is 9.3 ppm. Since the central electron spin resonance (ESR) linewidth HL is comparable with H0γC/γe, flip–flip and flip–flop forbidden transitions take place simultaneously. Consequently thermal mixing plays an important role in the 13C signal enhancement. However, the 13C spin-lattice relaxation rate is determined to a large extent by the solid state effect (forbidden transitions). The 13C polarization rates have been measured for the suite of diamonds by executing dynamic nuclear polarization (DNP) experiments on both hyperfine and central ESR lines. It is shown that the polarization rate is proportional to the paramagnetic impurity concentration of the sample, in agreement with the existing theory. It has been found that in type Ib diamonds with relatively low nitrogen impurity concentrations the dynamic nuclear polarization of a single hyperfine line yields an equilibrium 13C polarization that is one-quarter of that obtained in the case of dynamic nuclear polarization of the central line. In samples containing P1 and P2 centers (type Ia), or in type Ib samples with relatively high concentrations of P1 centers, the same equilibrium 13C polarization is obtained for the DNP of hyperfine and central transitions. This phenomenon is explained in terms of a model in which thermal contact is established between the electron Zeeman reservoir and the nuclear spin reservoirs via the spin–spin interaction reservoir if HL⩾H0γC/γe.

Preparation of 10 kg Ingot of Ultra-Pure Iron

A new induction melting furnace with a cold-copper crucible has been designed and constructed using ultra-high vacuum technology. The main chamber can be evacuated to 6.7 × 10—8 Pa as the base pressure. The furnace can melt high-purity iron of 10 kg, at most, within 300 s. The total pressure becomes less than 4 × 10—6 Pa during melting of iron under the best condition. As starting materials for melting, high-purity electrolytic iron containing impurities of 25.2 massppm which is determined after the analysis of 18 elements was prepared. The content of gaseous impurities such as carbon, nitrogen, oxygen, sulfur and hydrogen is 19.6 massppm in total. It is concluded that ultra-high vacuum melting of iron is quite useful to increase the purity of iron. The total content of impurities in iron is reduced from 25.2 to 12.6 massppm by melting under the atmosphere of 7.5 × 10—6 Pa. The amount of gaseous impurities can be reduced from 19.6 to 10.1 massppm in total. Especially, the amount of oxygen is reduced from 14.1 to 7.5 massppm. These amounts of gaseous impurities are almost the limit of detection by conventional methods of analysis.

Preparation of high purity alkali metals by near melting point segregation

Pure alkali metal preparation is a complex problem: in most available commercial samples, all of them are simultaneously present. Conventional separation techniques are not always effective enough to reach parts per million total impurity levels. However, near the melting point, superficial segregation occurs. A zone melting derived technique coupled with a specifically developed solvent extraction process allows the total impurity content of sodium to be lowered below a few parts per million. The described thermal process, although using chemical reactions, is purely physically steered: it purifies as well potassium containing sodium as sodium containing potassium. 4 alkali metals are considered: Li, Na; K, and Cs.

The dependences of ESR line widths and spin - spin relaxation times of single nitrogen defects on the concentration of nitrogen defects in diamond

Line widths and spin - spin relaxation times of P1 centres in synthetic Ib and natural Ia diamonds with concentrations of P1 and P2 centres covering the range 0.03 - 400 atomic parts per million have been measured. At concentrations higher than about ten atomic parts per million the line width is linearly dependent on the concentration. At lower concentrations the electron - dipolar contribution to the line width dominates and the width of the line remains constant. Since the pulse sequence employed for measurements eliminates the effects of inhomogeneous line broadening, of the line remains linearly dependent on the total paramagnetic impurity concentration, even at very low paramagnetic impurity concentrations.

Swelling, strengthening and embrittlement of beryllium under neutron irradiation to a fluence of 1.72 × 10 21 n/cm 2 ( E ≥ 0.85 MeV) at a temperature of 330–350°C. The role of main structure factors

Nine modifications of sintered (distilled and technical) beryllium were irradiated, investigated and compared. The major changes as a result of irradiation were shown to be variation of density, an increase in strength properties and decrease in plasticity properties. An expression that links swelling or additional sintering of the material with its initial porosity, total impurity content and mean grain size has been suggested.

Heat-capacity comparison among the nanocrystalline, amorphous, and coarse-grained polycrystalline states in element selenium.

Nanocrystalline element selenium ~nc-Se! samples were synthesized by completely crystallizing a meltquenched amorphous selenium ~a-Se!. Heat capacities ( Cp) of the nc-Se ~with a mean crystallite size of 10 nm!, a fully relaxed a-Se, and a coarse-grained polycrystalline Se were experimentally determined in a temperature range of 225‐500 K. Measurement results show that there is no pronounced difference between the Cp values of the nc-Se and the a-Se below 250 K. Heat capacities of the nc-Se are found to be only about 2% higher than those of the coarse-grained polycrystalline selenium. The Cp enhancement for the nc-Se, which is much lower than those reported in other nanocrystalline elements, is discussed in terms of the grain-boundary configurations in the nanostructures. @S0163-1829~96!02030-9# Heat capacity of a material is directly related to its atomic structure, or its vibrational and configurational entropy which is significantly affected by the nearest-neighbor configurations. Nanocrystalline ~nc! materials are structurally characterized by the ultrafine crystalline grains, and a large fraction of atoms located in the metastable grain boundaries in which the nearest-neighbor configurations are much different from those in the crystallites. Or in other words, the grain-boundary possesses an excess volume with respect to the perfect crystal lattice. Therefore, heat capacities of the nc materials are expected to be higher than those of the corresponding coarse-grained polycrystalline counterparts. Experimental measurements of heat capacities at constant pressure, Cp in several nc materials synthesized by means of different methods indicated that C p values are frequently higher than those for the coarse-grained polycrystalline counterparts, and are even higher than those for the amorphous states as well. 1‐3 For example, the Cp values of a nc-Pd synthesized by consolidation of ultrafine metal powders were reported to be as much as 60% higher than those for the coarse-grained polycrystalline Pd. 1 The heat-capacity values of a ball-milled nc-Ru sample were found to be about 20% higher than those of its coarse-grained polycrystalline counterparts. 2 Nevertheless, these results should be accepted cautiously because the measured Cp values might be influenced by many factors. Porosity and possible gaseous contamination @e.g., the sample has a density of only 80% and a total impurity content of about 1 at. % in the case of the nc-Pd ~Ref. 1!# in the ultrafine-powder-consolidated nc materials may contribute to the enhanced Cp . While in the ballmilled nc specimens, contamination from the milling media and the subsequent consolidation conditions might alter the heat-capacity results. Up to now, solid experimental results of heat-capacity comparison among the amorphous, the coarse-grained polycrystalline, and the nc states are still lacking.

Preparation of carbon incorporated NbAl alloy and its subsequent conversion to pure niobium by electron beam melting

Aluminothermic reduction of niobium pentoxide coupled with either direct electron beam melt refining of thermit niobium or a combination of pyrovacuum treatment of thermit niobium followed by electron beam melt refining of niobium sponge are the most widely adopted processes for the production of high purity (greater than 99.9 wt.%) niobium metal. Prior to pyrovacuum treatment, the thermit niobium ingot is crushed to smaller size of the order of 6 to 8 mm. Owing to very high hardness of thermit ingot, the crushing has been found to be quite difficult and energy intensive. The effectiveness of electron beam melt refining of thermit niobium is directly dependent on residual aluminum and oxygen concentration in the feed, which are inversely related. In the present studies, it has been found possible to eliminate problems encountered during crushing of thermit niobium as well as the pyrovacuum step by incorporating a judicious amount of carbon in the thermit niobium. A modified charge composed of niobium pentoxide, aluminium reductant corresponding to 10 wt.% excess over the stoichiometric amount and carbon amounting to 1 wt.% of Nb 2O 5 when reacted, resulted in a product alloy of NbAlC with higher niobium recovery (equal to or greater than 99 wt.%) and low residual aluminium concentration (less than or equal to 2 wt.%). It has been observed that the presence of carbon has not affected the overall yield. Carbon in the form of NbC preferentially precipitated at the grain boundaries of thermit alloy and rendered it easily crushable. Crushed alloy product could be subjected to direct electron beam melt refining without undergoing a pyrovacuum treatment step. No operational problems have been encountered, and in fact residual carbon assisted deoxidation in the final stage of electron beam melt refining. The electron beam melted button exhibited a hardness value of 65–70 VPN and a total impurity concentration of less than 0.05 wt.%.

Cross validation of capillary electrophoresis and high-performance liquid chromatography for cefotaxime and related impurities

A micellar electrokinetic chromatography method is presented which permits separation of cefotaxime and its major related impurities. Separation was carried out at 15 kV, using 30 mM sodium dihydrogen phosphate adjusted to pH 7.2 with 5 M NaOH and which contained 165 mM sodium dodecylsulfate as electrolyte. Results obtained by capillary electrophoresis were in good agreement with those of high-performance liquid chromatography with respect to the level of the major known impurities, total impurity content and cefotaxime purity.

A Survey of the Stability of Omeprazole Products from 13 Countries

The results of an independent survey of the stability of omeprazole solid dosage forms (20 mg) show that products available in many countries worldwide exhibit a very wide range of stability characteristics. Stability testing under the ICH accelerated test conditions (40°C/75% RH; 6 months) was performed on a total of 34 products obtained in 13 countries by independent sampling officers. The samples were visually examined for physical change and analyzed for their total content of impurities, remaining omeprazole, and the amount of omeprazole released in vitro. Twenty-seven of the products (79%) exhibited a change in one or more of the stability-indicating parameters during the 6-month study. These included 16 products that had more than 10% of decomposition products at 6 months and 10 other products that contained 2-10% of decomposition products at 6 months. In most samples, the formation of decomposition products was accompanied by a corresponding measurable decrease in the content of omeprazole. Of the eight samples containing less than 2% of decomposition products after 6 months storage, one showed a large reduction in the amount of omeprazole released in vitro. Another product which contained 1.2% decomposition products at 6 months released lower amounts of omeprazole in vitro at all time points than most other products. Only six products (18%) were considered to demonstrate good physical and chemical stability over the course of the study, viz. Losec Capsules (Astra, Sweden), Losec Capsules (Astra, Korea), Losec Capsules (Astra, Turkey), Miracid Capsules (Berlin Pharm. Ind. Co., Thailand), Mopral Capsules (Astra-Ifesa, Spain), and OMP Tablets (Chon Kun Dang Corp., Korea).

Ductility of Ultra High Purity Copper

The ductility of ultra-high purity copper at elevated temperatures was investigated : purity 99.9999% (6N) and 99.999999% (8N). Tensile tests were conducted at temperatures ranging from 293K to 1073K at strain rates of 4.2x10 -5 s -1 in a high vacuum. The results are discussed in comparison with those for 99.9% (3N) copper. Ductility at intermediate temperatures was improved by an increase in purity. The temperature at which ductility dropped decreased with increases in purity. Even at the ultra-high purity of 8N, a small ductility drop was observed at 423K. A small number of micro voids were observed on the grain boundaries of 8N specimens after the test at 423K. 6N and 8N copper have nearly same sulphur content of about 0.015 ppm. The intermediate temperature embrittlement of these coppers might be affected not only by sulphur content, but also by total impurity content.