共查询到20条相似文献,搜索用时 140 毫秒
1.
2.
3.
微波消解电感耦合等离子体光谱法测定碳化硼中痕量杂质元素 总被引:1,自引:0,他引:1
1引言碳化硼(B4C)陶瓷由于具有极高的硬度、优异的耐磨性能、优良的高温稳定性和化学稳定性以及轻质等优良特性而受到人们的极大关注,已在某些领域内得到了广泛应用。研究表明碳化硼中微量乃至痕量杂质元素都会影响其性能。电感耦合等离子体原子发射光谱法(ICP-AES)分析通常要求将样品处理成溶液雾化进样分析。在常压常温下,即使使用氢氟酸、碳化硼也难于分解。熔融样品则会引入大量的熔剂,需要稀释制样,影响样品痕量元素检测,且要使样品完全分解和分析也比较困难。本实验使用微波高压消解系统消解碳化硼样品,并用ICP-AES测定了碳化硼… 相似文献
4.
在化学分析中的某些情况下,一个溶样方法的选择,决定了测定的成败(如铱合金分析)。为了分析试样、试剂合成或制备标准溶液而常采用的热压分解法(其中包括玻璃封管法及压力溶样器法)是贵金属分析中分解试样的重要方法之一。已有文献介绍,方法是将试样与溶剂一起密封后,在加热的条件下,溶剂蒸气压增大,从而大大提高了试样分解的效率,加快了分解速度又节省了溶剂。是分解贵金属、稀有金属、合金、矿物及有机物等试样的有效方法。 相似文献
5.
6.
7.
8.
天青石、硅酸盐及其它矿物试样中锶的测定多采用碱熔分解,这不但手续繁长,且引入大量盐类,不利于用原子吸收或ICP法测定。我们在绵拔邦彦工作的基础上,试验了用氢碘酸-氢氟酸分解试样,并拟定了分解条件。以人工合成试样进行实验,结果回收率达99.5—101.2%,表明分解试样完全,效果好。并且与碱熔法的测定结果作了对照,测定值基本吻合。利 相似文献
9.
一般来说,贵金属试样的分解比其它常见金属困难。在应用的几种分解方法中,酸溶法一般只能分解银、金、钯、铂及其矿物;所有贵金属试样虽然都可用碱、硫酸氢盐或过氧化物等熔融分解,但将引入大量盐类及坩埚腐蚀带来的杂质;干法氯化能分解贵金属及矿物,但氯化装置复杂,不适于大批试样分 相似文献
10.
锂-硅粉末合金中锂、硅的重量配比要求较严,所以准确测定硅含量非常重要。过去,采用水解法分解试样,以重量法测定硅,这种方法反应异常剧烈,操作危险,且分析步骤繁琐。我们经试验拟定了水蒸气氧化分解试样,以差示分光光度法测定高含量硅。方法简便,溶样十分安全,适用于锂-硅粉末合金中含量高达50%硅的测定。实际试样分析获良好结果。 相似文献
11.
12.
D. Lezhava G. Darsavelidze D. Gabunia O. Tsagareishvili M. Antadze V. Gabunia 《Journal of solid state chemistry》2006,179(9):2934-2938
Temperature and amplitude dependences of dynamic shear modulus (SM) and of internal friction (IF) have been measured on boron carbide samples with different carbon content. The samples were investigated at frequencies of torsion oscillations from 0.5 to 5 Hz and at amplitudes of oscillatory deformation from 5×10−6 to 1×10−2 at temperatures from 80 to 1000 K. It was shown that absolute values of SM, of critical amplitudes of oscillatory deformation and of shear elastic limit decreased with the decrease of carbon content in the samples. Simultaneously, activation energy of the intensive relaxation-type IF in the vicinity of 450-470 K was also decreased. Cyclic deformation at 1000 K provided additional decrease to physicomechanical characteristics while at annealing in vacuum at the temperatures of 1273 and 1773 K these structure-sensitive properties significantly increased. The observed changes of physicomechanical characteristics were attributed to possible changes of inter-atomic forces in the structure of boron carbide samples. 相似文献
13.
The present communication is concerned with the effect of the carbon source on the morphology of reaction bonded boron carbide (B4C). Molten silicon reacts strongly and rapidly with free carbon to form large, faceted, regular polygon-shaped SiC particles, usually embedded in residual silicon pools. In the absence of free carbon, the formation of SiC relies on carbon that originates from within the boron carbide particles. Examination of the reaction bonded boron carbide revealed a core-rim microstructure consisting of boron carbide particles surrounded by secondary boron carbide containing some dissolved silicon. This microstructure is generated as the outcome of a dissolution-precipitation process. In the course of the infiltration process molten Si dissolves some boron carbide until its saturation with B and C. Subsequently, precipitation of secondary boron carbide enriched with boron and silicon takes place. In parallel, elongated, strongly twinned, faceted SiC particles are generated by rapid growth along preferred crystallographic directions. This sequence of events is supported by X-ray diffraction and microcompositional analysis and well accounted for by the thermodynamic analysis of the ternary B-C-Si system. 相似文献
14.
Densification of boron carbide during sintering may be improved by a two-stage process, namely heating to 2000°C under vacuum and sintering at 2190°C under argon. This sintering regime allows achieving a relative density of the ceramic bodies fabricated from a fine powder higher than 95%. The nitrogen treatment of the boron carbide phase at 1900°C leads to the formation of the BN phase and precipitation of graphite. Vacuum treatment of these samples at 2000°C leads to decomposition of the boron nitride phase. The liberated free boron may again react with graphite to form in situ boron carbide particles. The experimental investigations of the sintering behavior of the boron carbide phase under various atmospheres supported the thermodynamic predictions regarding the phase transformation. No evidence, however, was found for enhanced sintering under a nitrogen atmosphere. 相似文献
15.
Some physical properties of compacted specimens of highly dispersed boron carbide and boron suboxide
Otar Tsagareishvili David Lezhava Levan Gabunia Luiza Kekelidze 《Journal of solid state chemistry》2004,177(2):596-599
Structure, shear modulus and internal friction (IF) of compacted specimens of boron carbide and boron suboxide have been investigated. Microtwins and stacking faults were observed along the {100} plane systems of polycrystalline specimens of boron carbide. Electrical conductivity of the specimens was that of p-type. Concentration of holes varied from 1017 to 1019 cm−3. The IF was measured in the temperature range 80-300 K. It was shown that the IF of boron carbide and that of boron suboxide were characterized with a set of similar relaxation processes. Mechanisms of the relaxation processes in boron carbide and boron suboxide are discussed in terms of the Hasiguti model of interaction between dislocations and point defects. 相似文献
16.
Porous boron carbide preforms, prepared with and without excess carbon, were infiltrated with a Cu-Si alloy. Contrary to unalloyed copper, the Cu-Si alloy wets and infiltrates the porous preforms. A thermodynamic analysis of the B-C-Cu-Si system indicated that a Si content of the alloy above 15 at% leads to the formation of SiC. At higher Si content, the composition of boron carbide in contact with the melt also changes towards higher boron content. Metallographic examination validated these conclusions. The SiC compound forms preferentially around the free carbon particles in preforms containing excess carbon, and also in the vicinity of carbide that did not contain any excess carbon. Eventually, SiC, a product of the reaction between the carbide and the melt, forms a continuous barrier that impedes completion of the reaction and accounts for the limited increase of hardness as a result of lengthy heat treatments. 相似文献
17.
Boron was chosen as fuel in view of its excellent thermodynamic values for combustion, as compared to traditional fuels. The problem of the boron in combustion is the formation of a surface layer of oxide, which delays the ignition process, reducing the performance of the rocket engine. This paper presents a high-energy fuel for rocket engines. It is composed of sintered boron (borides and carbides and vitreous compounds) with a reducing chemical agent. Borides and boron carbide were prepared since the combustion heat of the latter is similar to that of the amorphous boron (in: K.K. Kuo (Ed.), Boron-Based Solid Propellant and Solid Fuel, Vol. 427, CRC Press, Boca Raton, FL, 1993). Several chemical reducing elements were used, such as aluminum, magnesium, and coke. As the raw material for boron, different compounds were used: amorphous boron, boric acid and boron oxide. 相似文献
18.
H. Werheit A. Leithe-Jasper T. Tanaka K.A. Schwetz 《Journal of solid state chemistry》2004,177(2):575-579
Large and high-quality floating zone grown single crystals of boron carbide of the composition B∼4.3C corresponding to the carbon-rich limit B4.3C of the homogeneity range, were presented by Leithe-Jasper and Tanaka at the ISBB’99 in Dinard for the first time. Such crystals now allow determining the physical properties of this refractory semiconductor free from the influence of impurities or coarse structural imperfections. Some solid-state properties of these single crystals like electronic transport properties, IR optical absorption spectrum, IR reflectivity spectrum, FT-Raman spectrum, and Knoop hardness are presented and discussed with respect to the properties of less perfect boron carbide previously determined. Outstanding properties are the hardness exceeding that of technical boron carbide by 14% (∥c) and 24% (⊥c) respectively, and the high optical absorption at energies below the absorption edge and the reflectivity strongly increasing towards low frequencies suggesting a destinctly higher contribution of free carriers. 相似文献
19.
Xiaopeng Jiao 《Journal of solid state chemistry》2010,183(7):1697-1703
Boron reacted with ball milled boron oxide under pressures between 1 and 5 GPa and at temperatures between 1300 and 1700 °C to afford boron suboxide (B6O). Icosahedral B6O grains with diameters ranging from 100 nm to 1.3 μm were prepared. The factors that affect the synthesis of B6O are investigated. The best sample with crystal size up to 1.3 μm is obtained at 2 GPa and 1400 °C for 6 h. The indentation experiment gave an average Vickers hardness of 32.3 GPa for bulk B6O sample, which is consistent with previous reports. Bulk B6O sample exhibits oxidation resistance in air up to 1000 °C and mild oxidation in the temperatures of 1000-1200 °C, which is more oxidation resistant than diamond. It is possible that B6O could be used as a substitute for diamond in industry because of its relatively mild synthesis conditions, high thermal stability and high hardness. 相似文献
20.
Yu. V. Pleskov M. D. Krotova V. V. Elkin E. A. Ekimov 《Russian Journal of Electrochemistry》2017,53(12):1345-1353
Substituting of metal (Co, Ni) borides for boron carbide in the boron carbide–graphite growth system for the process of diamond growth in the region of diamond thermodynamic stability allowed lowering the synthesis temperature for the electrodes of this new electrode material―boron-doped diamond compacts―significantly (by ~1000°C) without any deterioration of their electrochemical properties. On the other hand, using of amorphous boron with finer grain as compared with the boron carbide, mixed with graphite, results in a marked increase of the electrodes’ electrochemical efficiency, due to increase in their roughness after the chemical removing of boron-containing inclusions from their surfaces. Thus obtained compact electrodes have wide potential window and low background current in supporting electrolytes, they are well reproducible. Special features of their electrochemical impedance spectroscopy are similar to those of the recently studied compacts synthesized on the basis of boron carbide. 相似文献