Ball-milled Samples Research Articles

Nanophase ZrAl solid solutions by mechanical alloying at elevated temperatures

The mechanical alloying of ZrAl binary system has been studied under different milling temperatures. X-ray diffraction, high-resolution transmission electron microscopy (HRTEM) and differential scanning calorimetry (DSC) have been utilized to investigate the average grain size, atomic strain, microstructure and thermal stability of the ball-milled samples. Our experiments reveal that the ultimate grain size of nanostructured materials prepared by ball milling is determined by two main factors: one is the density of structural defects and another is the chemical composition. The grain size of a nanocrystalline supersaturated solid solution is stable under heat treatment until reaching the temperature where crystallization of an equilibrium compound phase occurs. The experimental results also suggest that the steady state obtained by ball milling at 300°C is determined by the metastable equilibrium of two phases, but the steady state reached by milling at room temperature is more homogeneous in chemistry.

Low temperature annealing of ball-milled Fe66B34

High energy ball-milling of Fe and B powders of starting composition Fe66B34 resulted in an alloy which revealed both a nanostructural state and a disordered amorphous-like state and a majority of unreacted components. The disordered phase is located in the interfacial regions between the Fe and B atoms. The ball-milled sample was annealed at low temperatures (250–350°C) to examine further the proposition that solid-state reaction is the mechanism of amorphization by mechanical alloying. A slight reaction between the Fe and B grains which were previously unreacted, probably limited to their contacting boundaries, has been detected.

Minimum Grain Size in Nanocrystalline Metal Powders

ABSTRACTNanocrystalline metal powders can be synthesized by mechanical attrition in a highenergy ball mill. A general relation determining the grain size of these materials is inferred. The ultimate grain size of nanocrystalline metals (typically 6 − 22 nm) is governed by the competition between the severe plastic deformation introduced during ball milling and the recovery behavior of the material. The lower bound grain size achievable by mechanical attrition is given by the minimum distance between two dislocations in a pile-up within a grain for all pure metals. Foar binary alloys the ultimate grain size depends on the composition of the material. Varying the composition changes the grain size reversibly. This can be explained by introducing solid solution hardening effects in the general relation for the lower bound grain size in pure metals. Thus, the proposed model for the ultimate grain size achievable by ball milling seems to be. applicable to all metals and alloys subjected to heavy mechanical deformation. However, reversible grain size changes are not restricted to mechanical attrition, but have also been observed for nanocrystalline Pd-H solid solutions produced by hydriding at constant pressure. Solid solutions prepared at different compositions, i.e. samples with different compositions, exhibit different grain sizes. Cycling between different temperatures/compositions changes the grain size reversibly. This cannot be explained by a model based on plastic deformation as in the case of ball-milled metal powders. The results are compared with data for ball-milled powders and samples prepared by inert gas condensation. The grain size changes are discussed with respect to the compositional changes and the grain boundary energy of the material.

Ball milling mechanical alloying in the Fe 100− xSi x system

Alloying and amorphization of ball-milled samples of nominal composition Fe 100− x Si x ( x = 5–50) has been investigated by means of X-ray diffraction, scanning electron microscopy, differential scanning calorimetry and magnetic measurements. An evaluation is made of the relative quantities of phases present in the as-milled samples.

Utilization of lignocellulose from barley straw by actinomycetes

The utilization and modification of grass lignocellulose was studied with actinomycete bacteria in liquid cultures. Ground and ballmilled barley straw samples were incubated with cultures of Streptomyces cyaneus, Thermomonospora mesophila and Actinomadura sp. MT809. High weight losses from both substrates were found after three weeks of incubation. S. cyaneus and T. mesophila also removed a part of the lignin in the straw residues. Water-soluble components released from the substrates did not accumulate in the supernatants but were partially utilised. The lignin-carbohydrate components isolated from both the residual and solubilised substrates showed pronounced differences in their chemical composition and changes in their molecular size distribution when compared to the untreated material.

PROCESSING STUDY OF HIGH TEMPERATURE SUPERCONDUCTING Y-Ba-Cu-O CERAMICS

Processing of the YBa{sub 2}Cu{sub 3}O{sub 6+x} superconducting phase by employing different precursor powder preparation techniques (ball milling, attrition milling) and samples formed by different sintering conditions are discussed. The superconducting phase has been identified by powder x-ray diffraction. The effect of different powder processing and pressing conditions on the structure, density, resistivity and a.c. magnetic susceptibility were studied. Though there is no variation in T{sub c} for all the samples, attrition milled samples show a much lower resistance and less temperature dependence compared to ball milled samples above the superconducting transition temperature up to room temperature. Ball milled samples were loosely packed with more voids compared to attrition milled samples which are more densely packed with a needle-like structure.

Factors Involved in the Cytotoxicity of UICC Amosite towards Macrophages

The cytotoxicity of various ball-milled UICC amosite samples toward mouse peritoneal macrophages in vitro was examined. On increased ball milling, the cytotoxicity of the amosite samples fell. This decreased biological activity seemed to correlate best with number of fibers longer than 4 micron/micrograms dust, rather than total number of fibers or the electrophoretic mobility of the amosite samples.

Factors involved in the cytotoxicity of UICC amosite towards macrophages.

The cytotoxicity of various ball-milled UICC amosite samples toward mouse peritoneal macrophages in vitro was examined. On increased ball milling, the cytotoxicity of the amosite samples fell. This decreased biological activity seemed to correlate best with number of fibers longer than 4 micron/micrograms dust, rather than total number of fibers or the electrophoretic mobility of the amosite samples.

Surface interaction in the [formula omitted] system

A rapid (1.5 h) one-step ball milling (BM) method was developed to synthesize VOx/TiO2 (VTi-BM) and WOx or MoOx doped VOx/TiO2 (VWTi-BM or VMoTi-BM). Catalytic activity on gaseous POPs removal was tested using hexachlorobenzene (HCB) as surrogate. Catalytic performance decreased in the order of VWTi-BM (T50% = 230 °C) > VMoTi-BM (260 °C) > VTi-BM (270 °C) > VTi-WI (300 °C; VOx/TiO2 synthesized by wetness impregnation method). The intermediates from oxidation of HCB were analyzed by off gas analysis, from which 2,2,4,5-tetrachloro-4-cyclopentene-1,3-dione (TCCD), dichloromaleic anhydride (DCMA) and tetrachloro-1,4-bezoquinone (TCBQ) were identified. Furthermore, a possible mechanism for the oxidation of HCB over VOx/TiO2 catalysts was proposed. Mechanism studies showed that BM samples possess better dispersion of the VOx species and more surface chemisorbed oxygen. Doping WOx or MoOx into VOx/TiO2 by ball milling can further enhance catalytic performance by increasing surface acid sites.

Isotopic exchange in solid cobalt phthalocyanine—I: Thermal treatment and charge transfer interactions

Isotopic exchange of α and ß-cobalt phthalocyanine (CoPc) doped with carrier-free 57CoCl 2 was studied at different temperatures in presence, and absence of oxygen. In samples sealed in evacuated vials, the exchange is induced by electrons released from multi-depth donors. The results show that ß-CoPc has a smaller density of donors and a deeper distribution in depths, as compared to α-CoPc. The mode of population of traps with electrons (or holes) during the preparation is discussed. Thermal treatment of CoPc in air and followed by doping with 57CoCl 2 (and radiochemical analysis) gives us the magnitude of isotopic exchange induced by holes, which are injected by virtue of charge transfer interactions between molecules of CoPc and O 2. Our observations indicate that the rate of diffusion of O 2 into CoPc crystallites depends on the temperature and the period of thermal treatment. The diffusion continues well beyond 1 week even at relatively high temperatures. The concentration of the injected holes and therefore the magnitude of exchange depends on the size of particles. The diffusion and chemisorption of O 2 seems to be facilitated considerably when the microcrystallites of CoPc are suspended in oxygenated water (as compared to the dry powder). When aliquots of 57Co 2+-doped CoPc are compacted with o-chloranil or iodine, strong charge transfer interactions between CoPc, and o-chloranil, and (to a lesser extent) iodine molecules, inject high concentrations of holes and thereby induce considerable exchange. When samples of 57Co 2+-doped α- or ß-CoPc are heated in air, either detrapped electrons or injected holes may induce exchange. In ball-milled samples, consisting of very fine particles, the contributions towards exchange by electrons and holes, become additive. This amazing observation indicates that large non-equilibrium concentrations of electrons and holes co-exist for considerable lengths of time without recombination. In conclusion, the dopant 57Co 2+ in CoPc constitutes a good probe and we have obtained a wealth of information which would be difficult to obtain by purely physical measurements.

Cleaning process for contaminated superalloy powders

A cleaning process for removing interstitial contaminants from superalloy powders after wet grinding is described. Typical analyses of oxygen, carbon, nitrogen, and hydrogen in ball-milled WAZ-20 superalloy samples after hydrogen plus vacuum cleaning are presented. The hydrogen cleaning step involves heating retorts containing superalloy powder twice under flowing hydrogen with a 24-hour hold at each temperature. The vacuum step involves heating cold-pressed billets two hours at an elevated temperature at a pressure of 10 microPa. It is suggested that the hydrogen plus vacuum cleaning procedure can be applied to superalloys contaminated by other substances in other industrial processes.

Disorder in cellulosic fibers

AbstractRuland's concept of an isotropic disorder function is applied to estimate the disorder parameter and the degree of crystallinity in a few cellulosic fibers: two cottons, native ramie, and a high‐tenacity rayon. The results indicate an increase in disorder without any change in crystallinity on mercerization of native celluloses. On hydrolysis, with or without a pretreatment of mercerization, the samples exhibit a higher crystallinity, disorder remaining the same as for native celluloses. A ball‐milled sample of “amorphous” cellulose is still found to be fairly crystalline with the lowest disorder. On being wetted in water and oven‐dried, a distorted form of cellulose II with higher crystallinity and disorder was obtained. The polynosic fiber, Tufcel, has low values for the degree of crystallinity, disorder parameter, as well as crystallite dimension. A strong dependence of the degree of crystallinity on the crystallite size, particularly the lateral, is observed.

Recovery of electroluminescence by ageing of ball milled powders

The paper studies the influence of ageing on the electroluminescence of ball milled powders of zinc sulphide and it is shown that partial recovery of the electroluminescence (EL) brightness of ball milled samples occurs. The EL brightness of a non-milled sample did not change with ageing. The recovery of EL ball milled samples is explained by the recovery of the EL barriers by diffusion of the copper ions which were dispersed over the crystallites of the EL powders by ball milling.

Comparison of Thermal Properties between Compact and Wet Ball-milled Rôseki (Pyrophyllite)

The pyrochemical properties of the naturally compact pyrophyllite from Shoko-Mountain were investigated in detail. The comparative study on ceramic properties was also made about cut-off samples and wet ball-milled samples.The mineralogical compositions of this sample were 23% fine-grained quartz, 4% sericite, and a little kaolinite. The ground sample lost the combined water between 400° and 800°C, and the compact sample between 500° and 900°C without breakdown of the crystal lattice, but the specific surface area, which was determined by BET method, gave the maximum value with 700°C fired sample. The specific gravity decreased from 500° to 800°C rapidly. The apparent porosity and the water absorption of the fired compact sample increased from 600° to 900°C, and then decreased slowly; but with the ball-milled sample these properties decreased from 900°C and rapidly from 1100°C. The fired volume change was also different, the compact sample indicated permanent expansion from 600° to 1400°C, but the ground sample contracted from 1000°C. The bending strength of the compact sample decreased rapidly from 1300°C, but the ground sample increased from 1200°C rapidly. Samples which were fired between 900° and 1300°C gave very low thermal expansion, but samples fired above 1350°C gave marked cristobalite effect. The moisture expansion of the compact sample which was fired above 1100°C showed almost negligible value, but under the 1100°C fired sample showed some degrees of moisture expansion. On the contrary, ground sample showed marked moisture expansion above 1100°C.

The Ceramic Property of Fukui Pottery Stones

The ceramic property of five kinds of Fukui pottery stones occured in Onigatake, Jogatani, Myohoji and Uesaka, was investigated.The mineralogical composition was identified by means of X-ray diffraction, D. T. A., chemical analysis and electron micrograph methods.The following properties were measured on 20hrs wet ball-milled samples, i.e. viscosity, plasticity, modulus of rupture, refractoriness and thermal expansion.Pressed specimens of the wet ball-milled sample were fired in the temperature range of 800 to 1300°C and determinations of firing shrinkage, thermal expansion, water absorption, reflection, modulus of rupture and moisture expansion were made on the fired specimens.

Effect of Particle Size upon the in Vitro Cellulose Digestibility of Forages by Rumen Bacteria1,2,3

Summary Rates of in vitro cellulose digestion were determined for mature timothy (seed ripe) which had been ball-milled 0, 6, 24, and 72 hr. The total amount of cellulose digested increased with the time of ball-milling up to 72 hr. Based on this observation four stages of timothy, three of alfalfa, and two each of brome and orchard grass, along with 72-hr. ball-milled samples of these same forages, were used as substrates for in vitro rumen fermentations. In all cases, ball-milling increased the amount of cellulose digested, and this increase became larger with advancing maturity and lignification of the forage. In further work, mature timothy was digested 48 hr. in vitro and the residue isolated. Less than 5% of the cellulose remaining in this residue was digested in a second 48-hr. fermentation; however, when a portion of this residue was ball-milled, 67% of the cellulose could be digested. Additional experiments which determined the amount of forage cellulose soluble in cupriethylene diamine, indicated that the amount of cellulose which can be dissolved decreases with forage maturity and increased deposition of lignin. The amount of cellulose dissolved was markedly increased after ball-milling, and again this increase became larger with advancing maturity of the forage. The experimental evidence presented in this paper substantiates the theory that the lignin in forages acts as a physical barrier between the cellulose and cellulolytic rumen bacteria.

On the draught, height and area of smoke pipes, etc.

CaF2:Dy phosphor was prepared by ball milling method over particle size ranging from 140 nm to 35 nm, and their thermoluminescence properties were studied by irradiation with 60Co gamma rays. The XRD revealed that the crystallite size was of ∼45 nm for pristine, 19.1 nm for 10 h and 9.99 nm for 50 h ball-milled phosphor samples and confirmed by FESEM. The UV–visible spectra indicate that the absorption and scattering of radiation increased with a decrease in the particle size along with the blue shift in the absorption peak. CaF2:Dy particles of different sizes were irradiated with gamma dose from 1 Gy to 20 kGy and respective thermoluminescence response was studied. It was observed that the ∼65 nm particle size phosphor showed a linear response with gamma dose range from 1 Gy to 12 kGy. These results reveal that the CaF2:Dy phosphor can be used for high gamma radiation measurement and food irradiation dosimetry.