钢球质量监测最佳抽检方案的确定

本文介绍概率抽样法在钢球生产过程中的应用,通过此法确定钢球生产中各工序质量监测的最佳抽检方案,以确保产品被接受的概率最大。     

Mechanosynthesis of YIG and GdIG: A Structural and Mössbauer Study

We have investigated the mechanosynthesis of gadolinium and yttrium iron garnets by high-energy ball-milling of α-Fe₂O₃ and Gd₂O₃ or α-Fe₂O₃ and Y₂O₃, respectively, followed by short thermal annealings conducted at moderate temperatures. The samples were characterized by X-ray diffraction and Mössbauer spectroscopy, in order to determine the influence of the milling time and annealing conditions on the final products. For as-milled samples of each rare-earth system, the results revealed the formation of perovskite phases, in relative amounts that depend on the milling time. The formation of garnet phases was observed in as-annealed samples treated at 1000°C for 2 h or 1100°C for 3 h, i.e., at very modest annealing requirements when compared with ordinary solid-state-reaction processes performed without previous high-energy milling. Also, the occurrence was verified of a milling time for which the relative amount of garnet phases formed by annealing was maximized. This time depends on the rare-earth composing the garnet phase and on the annealing temperature.     

WS2 超细粉体的固相法合成

WS2 超细粉体的固相法合成;WS2;固相反应;过硫系数;高能球磨;粒度     

机械球磨与反应烧结合成Sr2CeO4发光体的研究

Sr₂CeO₄ phosphor was synthesized by mechanical milling and reactive sintering in this work. The solid state reaction of SrCO₃and CeO₂ (2∶1) started at about 850 ℃ and completed at 1 000 ℃ for about 4 h. Two types of formation mechanism of Sr₂CeO₄ were proposed. When the starting powder mixture was fired above 1 000 ℃, the unstable intermediate phase SrCeO₃was developed, which then reacted with SrCO₃to form the final product Sr₂CeO₄, however, SrCO₃and CeO₂ converted directly to Sr₂CeO₄ at a lower temperature. The XRD results showed the crystal structure of Sr₂CeO₄ was orthorhombic. The emission spectra displayed a broad band with maximum at about 465 nm. The mechanical milling of starting power mixture and the sintering temperature had no effect on this emission spectra.     

Conversions between ordered and disordered cellulose. Effects of mechanical treatment followed by cyclic wetting and drying

An investigation into the effects of mechanical treatment and hydration on the order of cellulose substrates (microcrystalline cellulose and Cladophora cellulose) was performed by the use of ball milling followed by cyclic wetting and drying. The results, monitored by¹³C-CP/MAS NMR-spectroscopy, were evaluated by calculation of the crystallinity indices and principal component analysis of the NMR data acquired. The results showed that a large part of the disorder induced by the mechanical treatment of cellulose by ball milling is reversible and reordering upon hydration leads to the cellulose I form initially present. The C4 signals corresponding to the reversibly disordered cellulose chains are observed in the amorphous region between 79 and 86 ppm in the¹³C-CP/MAS NMR-spectra together with signals from cellulose chains on the surface of ordered regions. The peak cluster which contains the C2, C3 and C5 ring carbons can be divided into two specific spectral regions; one between 74 and 77 ppm largely originates from ring carbons within disordered cellulose structures, and one between 70 and 74 ppm contains larger contributions from ordered cellulose. The behaviour of the celluloses upon milling is in accordance with a concept of ordered cellulose fibrils containing amorphous cellulose mainly as surface layers and induced reversible lattice distortions.     

Reactivity and Structural Properties of a Mechanochemically Treated Ag2O-V2O5 System in Relation to AgVO3 Polymorphs

Formation and chemical properties of amorphous AgVO₃, which was prepared by mechanochemical treatment of an Ag₂O-V₂O₅ mixture, and crystalline AgVO₃ were studied in relation to AgVO₃ polymorphs. A ball-milled sample of the mixture was assigned as a highly deformed β-AgVO₃ rather than the low density phase α-AgVO₃. Crystalline α-AgVO₃ and β-AgVO₃ were converted into deformed β-AgVO₃ by ball milling, which produced a clear change. δ-AgVO₃ is resistant to mechanical treatment and its structure was not markedly affected. The dissolved chemical species from the ball-milled sample precipitates to form α-AgVO₃ without a seeding crystal, but other polymorphs deposit if they are present; i.e., β-AgVO₃ and δ-AgVO₃ grow on the seeding crystal.     

Enhancing the enzymatic hydrolysis of cellulosic materials using simultaneous ball milling

One of the limiting factors restricting the effective and efficient bioconversion of softwood-derived lignocellulosic residues is the recalcitrance of the substrate following pretreatment. Consequently, the ensuing enzymatic process requires relatively high enzyme loadings to produce monomeric carbohydrates that are readily fermentable by ethanologenic microorganisms. In an attempt to circumvent the need for larger enzyme loadings, a simultaneous physical and enzymatic hydrolysis treatment was evaluated. A ball-mill reactor was used as the digestion vessel, and the extent and rate of hydrolysis were monitored. Concurrently, enzyme adsorption profiles and the rate of conversion during the course of hydrolysis were monitored. α-Cellulose, employed as a model substrate, and SO₂-impregnated steam-exploded Douglas-fir wood chips were assessed as the cellulosic substrates. The softwood-derived substrate was further posttreated with water and hot alkaline hydrogen peroxide to remove >90% of the original lignin. Experiments at different reaction conditions were evaluated, including substrate concentration, enzyme loading, reaction volumes, and number of ball beads employed during mechanical milling. It was apparent that the best conditions for the enzymatic hydrolysis of α-cellulose were attained using a higher number of beads, while the presence of air-liquid interface did not seem to affect the rate of saccharification. Similarly, when employing the lignocellulosic substrate, up to 100% hydrolysis could be achieved with a minimum enzyme loading (10 filter paper units/g of cellulose), at lower substrate concentrations and with a greater number of reaction beads during milling. It was apparent that the combined strategy of simultaneous ball milling and enzymatic hydrolysis could improve the rate of saccharification and/or reduce the enzyme loading required to attain total hydrolysis of the carbohydrate moieties.     

纳米晶掺钇硬质合金粉末的制备

采用高能球磨法制备了纳米晶掺Y硬质合金粉末。用XRD，SEM和DTA等分析检测手段，研究了纳米晶掺Y硬质合金粉末的结构、形貌和相的变化。结果表明：高能球磨45h，可获得晶粒尺寸约为8nm的掺Y硬质合金粉末；微量Y的加入，有利于硬质合金粉末晶粒的细化；在25～45h范围内，随着高能球磨时间的延长，粉末晶粒尺寸减小，且掺Y硬质合金粉末的晶粒尺寸比未掺Y的硬质合金粉末晶粒尺寸要细一倍；高能球磨25h，粉末中Co的X射线衍射峰消失。高能球磨掺Y硬质合金粉末的DTA曲线在626℃出现了1个尖锐的放热峰。高能球磨掺Y硬质合金粉末固结之后，其合金晶粒细小，机械性能较好。     

Small ball probabilities for a Wiener process under weighted sup-norms,with an application to the supremum of bessel local times

LetR be the radial part of ad-dimensional Wiener process, starting from 0. In this paper, small ball probabilities are evaluated for sup_0<11(t ^–p R(t)) and sup _t 0(e ^–1 R(t)), withp[0, 1/2]. Chung's law of the iterated logarithm is established for the supremum of the local times of a two-dimensional Bessel process.     

Are the pyrazolines formed from the reaction of [60]fullerene with alkyl diazoacetates unstable?

[60]Fullerene-fused pyrazolines 1 were prepared by the reaction of C₆₀ with alky diazoacetates under the solid-state high-speed vibration milling conditions as well as in toluene solution. Pyrazolines 1 were stable in refluxing toluene and its thermolysis process in 1,2-dichlorobenzene was investigated, the decomposition rates and activation energies of pyrazolines 1 were obtained. The current work demonstrated that the liquid-phase reaction of C₆₀ with alkyl diazoacetates undergoes via 1,3-dipolar cycloaddition pathway at room temperature, or proceeds via carbene mechanism at a temperature of refluxing toluene, thus clarifies the previous ambiguity of its reaction mechanism.