Neste trabalho, investigou-se a elaboração mecânica do composto intermetálico TiFe por moagem de bolas com alta energia. Uma forte aderência do material moído, particularmente nas paredes do recipiente de moagem, foi o principal problema verificado com tempos de moagem superiores a 1 hora (moinho agitador). Tentativas para resolver este problema foram realizadas inicialmente com o emprego de agentes controladores de processo (ACPs), como etanol, ácido esteárico, polietileno de baixa densidade, benzeno e ciclohexano, em diferentes quantidades (1 a 20% em massa) e tempos (1 a 40 h), mantendo-se constantes outros parâmetros de moagem como a razão bola:pó em massa (10:1) e o tamanho das bolas (=7mm). Os rendimentos mais elevados (em termos da massa de pó não aderido) foram obtidos quando se utilizaram grandes quantidades de benzeno e ciclohexano (101 e 103% em massa, respectivamente), porém com a formação de TiC ao invés de TiFe em razão da decomposição do ACP e reação do carbono com as partículas de titânio. As moagens foram realizadas posteriormente sem o emprego de qualquer ACP e também utilizando um moinho planetário. Várias estratégias foram investigadas para se tentar mitigar a aderência incluindo-se: (a) moagem de uma pequena quantidade da mistura de pós de Ti e de Fe, revestindo as paredes do recipiente e as bolas de moagem, antes da moagem da carga principal, (b) moagem pausada com aberturas intermediarias do recipiente em atmosfera ambiente, (c) moagem pausada para rotação e inversão da posição do recipiente de moagem (apenas no moinho agitador), (d) moagem isolada dos pós de Ti e de Fe, antes da moagem da mistura, e (e) moagem do pó de Fe com o Ti hidretado. Os melhores resultados, em termos de diminuição da aderência combinada com a formação majoritária do composto TiFe durante a moagem, foram obtidos quando se adotou o procedimento de inversão/rotação, juntamente com o processo de revestimento preliminar do recipiente e das bolas de moagem (26% em massa). Rendimentos maiores foram obtidos com a utilização do TiH2 no moinho planetário, porém sem a formação majoritária do TiFe durante a moagem. / In this work an investigation on the mechanical alloying of the intermetallic compound TiFe by high-energy ball milling was conducted. Strong adherence of milled material, particularly at the vial walls, was seen to be the main problem at milling times higher than 1 hour (shaker mill), hindering the compound synthesis. Attempts to prevent this problem were accomplished first by adding different process control agents (PCAs), like ethanol, stearic acid, low density polyethylene, benzene and cyclohexane at variable quantities (1 to 20 wt. %) and times (1 to 40 h), keeping constant other milling parameters like ball to powder mass ratio (10:1) and balls size (=7mm). Highest yields (related to the non adhered powder) were attained with larger amounts of benzene and cyclohexane (101 and 103 wt. %, respectively), but with TiC formation during milling instead of TiFe due to the PCA decomposition and the reaction of the carbon with and titanium particles. Milling was conducted further without adding any PCA and also using a planetary ball mill. Several strategies were tried to avoid or minimize the adherence including: (a) milling of a small quantity of the Ti and Fe powder mixture, dirtying the vial walls and the balls surfaces before milling the main charge, (b) stepwise milling with intermediate openings of the vial in air, (c) stepwise milling with the rotation and the inversion of the vial position between the steps (only in the shaker mill), (d) milling Ti and Fe powders (apart from each other) before milling the mixture of them, and (e) milling Fe powder with Ti hydride powder. Best results concerning both yield and major TiFe formation during milling were verified with the rotation/inversion procedure combined with preliminar dirtying of the vial and balls (26 wt.% in the shaker mill). Higher yields could be attained by using TiH2 powder in the planetary mill, but with no major TiFe formation during milling.

Durante o período de operação de um empreendimento mineiro, oportunidades de aumento de capacidade produtiva podem gerar ganhos significativos para uma empresa. Para os casos em que se viabiliza maior capacidade de produção da mina deve-se avaliar a capacidade de processamento da usina de beneficiamento, que assim inclui melhorias de desempenho ou expansão mediante adição de equipamentos. Este trabalho contempla a descrição das etapas de amostragem, caracterização do minério, a modelagem do circuito existente e a simulação para aumento da capacidade do circuito de moagem da usina da Mineração Serra Grande da AngloGold Ashanti, situada no município de Crixás no interior de Goiás. Os cenários simulados foram (1) adição de um terceiro moinho de bolas em série aos moinhos existentes, (2) adição de um terceiro moinho de bolas em paralelo ao circuito existente, (3) adição de um moinho vertical para processamento do produto dos dois moinhos de bolas existentes e (4) adição de uma prensa de rolos após o circuito de britagem. O propósito das quatro simulações foi avaliar a viabilidade técnica dos circuitos selecionados mediante modelagem matemática e simulação de processos, assim como dimensionar os novos equipamentos para tal fim. / During operation of the mining cycle, increases the throughput would generate significant capital savings for a company. For cases that enables higher mine production capacity, it must be evaluated plant capacity and also performance improvements or expansion by adding new equipment. This study includes the description of the sampling methodology, the minerals analysis, modeling of the existing circuit and simulation for a possible expansion, specifically for the grinding circuit at Mineração Serra Grande plant of AngloGold Ashanti group, located in Crixás, Goiás. the studied scenarios were: (1) adding a third ball mill in series with existing two ball mills, (2) adding a third ball mill in parallel with existing mills, (3) adding a vertical mill in series with existing mills and (4) adding high pressure grinding rolls to existing mills. The four simulations intend assess the technical feasibility of the circuits selected by mathematical modeling and simulation of processes and design new equipment for this purpose.

Thesis (Ph. D. (Physics)) -- University of Limpopo, 2013 / A combination of ball milling experiments and ab initio calculations in this study successfully yielded results that shed light into understanding the fundamental basis for immiscibility and the concept of mechanical alloying in Ti-Mg system. In addition, the conditions for achieving extended solid solubility in elements that usually do not dissolve in each other under thermodynamic equilibrium conditions have been predicted using ultrasoft (US) and norm-conserving (NC) pseudopotentials. Hydostatic pressures required to stabilize ordered phases were determined. Our new systematic representation of martensitic transformation (MT) paths as a result of dislocation necessary to induce α→FCC, α→BCC and α→ω phase transitions led to, for the first time, a direct determination of CRSS and tensile strength for Ti and Mg HCP metals. Furthermore, a new ω phase which is less stable than α phase at 0 GPa is proposed. Based on this phase, α→ω deformation path which yielded the onset of uniaxial transition pressure of 4.167 GPa is reported. Attempts of synthesizing Ti-Mg solid solutions by means of Simoloyer high energy ball mill were not successful; however, nanocrystalline Mg-TiH2-x composites were instead formed. These results were attributed to quick formation of metastable Ti hydrides or cold welding at early stages of BM prior to alloying, thus serving as possible obstacles to forming such solid solutions. The deformed Ti crystals adsorbed H+ from the stearic acid leading to formation of metastable orthorhombic TiH2-x phase which later transformed to a tetragonal TiH2-x or even cubic TiH2 when stoichiometric amount of H2 had been adsorbed. Although the yield was significantly lower, the product of milling a mixture of coarse Mg and fine Ti particles was comprised of Ti particles adhering around ductile Mg particles in a core shell manner. The adhesion of the fine hard titanium particles on the surface of the large ductile magnesium particles impeded the further plastic deformation of the titanium particles, thus suppressing the formation of the faults necessary for mechanical alloying. Nanocrystalline Ti powder of about 40 nm was produced by 30h ball milling. During BM of Ti powder, solid-state transformation from HCP to FCC occurred in the presence of PCA with lattice parameters of 4.242 and 4.240 Å after 24 and 30 h, respectively, v due to protonation. When Ti powder was milled in the absence of PCA, no phase transformation was observed for both uninterrupted and interrupted milling cycles. In addition, nanocrystalline Mg powder with crystallite size varying between 60 and below 40 nm was produced by ball milling. However, no solid-state transformation took place even if the powder was milled for 90 h. Therefore, we evidently report for the first time that the interstitial H+ is the driving force for α → FCC phase transformation in ball milled Ti powder. Our theoretical results predicted the ω phase to be the ground-state structure of Ti at 0K and P=0 GPa, in support of other previously reported calculations. We noticed that the stability of the α phase was surpassed by that of the FCC lattice at ~ 100 GPa, corresponding with sudden sharp rise in c/a ratio, hence attributed to α → FCC phase transition. Similar results were obtained for Mg at 50 GPa, although in this case the crossing of lattice energies coincided with minimum c/a. However, using our proposed HCP→BCC MT path mechanism for Mg, it is evident that the minimum c/a at 50 GPa corresponds to a change in the preferred deformation slip from basal (below 10 GPa) to prismatic rather than phase transition. Nonetheless, the proposed MT model predicts that both elemental Ti and Mg prefer to deform via prismatic slip as indicated by lower shear stress as well as CRSS values compared to those calculated for basal slip. Theoretical findings from ab initio calculations on hypothetical ordered Ti-Mg phases indicated absence of intermetallic phases at equilibrium conditions, in agreement with experimental data. However, the formation becomes possible at 80 GPa and above with respect to c/a ratio but requires at least 200 GPa with respect to stable lattices. Using calculated heats of formation, elasticity and DOS, it has been possible to show that L12 TiMg3 could not form even at high pressure as 250 GPa. Nonetheless, both approaches indicate that forming an intermetallic compound between Ti and Mg requires a crystal structure change, α→FCC for Ti and HCP→BCC for Mg. Proposed DFT-based solid solution model for predicting phase stability and elastic properties of binary random alloys, with Mg-Li system serving as a test case, successfully yielded reliable results comparable to experimental data. This method was successfully applied to study an immiscible Ti-Mg system and the solubility limit vi was for the first time theoretically established. Based on formation energy of Ti-Mg solid solutions, our calculations predicted for the first time that the solubility of up to 60 and 100 at.% Mg into Ti with the use of USP and NCP, respectively, to be thermodynamically favourable with necessary lattice kinetics being the main challenge. Nonetheless, NCP proved to be reliable in predicting structural and elastic properties of disordered alloys.

Previous work has shown that when inorganic compounds are milled with quartz in a high energy ball mill the elements are sequestered into the quartz matrix and cannot be easily recovered by simple extraction methods. In this study lead (II) oxide, copper (II) oxide, magnesium oxide, zinc oxide and sodium hydroxide were milled with quartz sand and the recoveries of the metals investigated in detail. The standard EPA3050B method (acid digestion of sediments, sludge and soils) for extractable metals was compared to exhaustive HF digestion method based on ASTM C146-94a (test methods for chemical analysis of glass sand) and UDC 666.123:543.06 (chemical analysis of soda-lime and borosilicate glass). From these two analyses the total recovery of metals was determined. It was found that the elements extracted by the EPA3050B method decreased in an approximately logarithmic way with milling time. The metals are apparently strongly sequestered into the fractured quartz. Total HF digestion of the insoluble matrix gave good recovery of the “lost” elements. A reliable analytical procedure has been developed and the mechanisms leading to this sequestering are discussed. Particle size analysis and electron microscopy of milled samples support a process of brittle alloy formation as the proposed mechanism whereby the elements are sequestered into the milled quartz.

In this thesis work, it was aimed to optimize the conditions to produce silicon carbide (SiC), from rice husks from Turkish Thrace Region, via pyrolysis. Rice husks, coked at 500oC, were high energy ball-milled prior to pyrolysis, in order to investigate the effects of ball-milling on pyrolysis temperature, pyrolysis time and morphology of the SiC produced. Samples of rice husks subjected to different ball milling conditions, were pyrolyzed at temperatures varying from 1500oC to 1600oC and for times varying from &frac12 / hour to 2 hours. Results of experiments showed that, ball-milling reduced the pyrolysis temperature and pyrolysis time to some extent. It was also experimentally shown that ball-milling favored the formation of SiC particles rather than formation of SiC whisker.

Compaction of polymer powders and polymer-based nanocomposites by uniaxial high-velocity cold compaction (HVC), by high-energy ball milling (HEBM) and using a novel technique, relaxation assists, was investigated with a focus on the process parameters, the compactibility characteristics, surface morphology and friction. The basic phenomena associated with HVC are explained and the general energy principle is introduced to explain the pull-out phenomenon, springback gradient, delay time, relative time of the pressure wave, and stick-slip phenomenon during the compaction process. Experimental results for different compaction profiles, different particle size distributions and different milling system for polymer-based nanocomposite are presented, showing the effect of varying the process parameters on the compacted material; the compactibility in the compacted bed, the uniformity of the compacted surface, the pull-out phenomenon, the springback gradient, the stick-slip phenomenon and the homogeneity of the dispersions of nanoparticles in the polymer powders in the solid state. It was found that the high-velocity compaction process is an interruption process and that the opposite velocity and pressure loss during the compaction process have a major influence on the quality of the compacted material. The relaxation assist device is a novel technique that has been successfully developed to improve the compaction process. The relaxation assists are parts of the piston and they are regarded as projectile supports. They are constructed of the same material as the piston, and the diameters are the same but the lengths are different. The relaxation assist device leads to an improvement in the compaction of powders, polymer powders and polymer-based nanocomposites by giving a more homogeneous opposite velocity and a better locking of the powder bed in the compacted form during the compaction process with less change in dimensions in the case of both homogeneous and heterogeneous materials. If the movement of the particles is restricted the powder bed attains a higher density and the total elastic springback is minimized. In addition, there is a more homogeneous dispersion of nanoparticles in the case of a heterogeneous material. A much better transfer of the pressure through the powder bed and a smaller loss of pressure lead to a more homogenous stick-slip of the particles and a higher sliding coefficient due to the overall friction during the compaction process. / QC 20100630

A titanium dioxide powder co-doped with boron and zirconium was prepared by mechanical ball milling. Photocatalytic performance of the powder was evaluated by degradation of methylene blue (MB) solution under UV illumination. XRD patterns were refined by Rietveld analysis method to obtain accurate lattice parameters and position of the atoms in the crystal structure of TiO2. XRD analysis indicated that the B and/or Zr doped TiO2 powders composed of anatase and did not exhibit any additional phase. Rietveld analysis suggested that dopant B and Zr elements were successfully weaved into crystal structure and distorted the lattice of TiO2. The highest distortion was obtained by co-doping. SEM investigations confirmed that mechanical ball milling technique led to a decrease in particle size of TiO2 powder. XPS analysis revealed that dopant B and Zr atoms did not appear in any form of compound including Ti and O elements. Results of photocatalytic activity test suggested that boron and zirconium co-doped TiO2 particles exhibited a better visible light response and photocatalytic activity than that of mono element doped TiO2 (i.e. B-TiO2 and Zr-TiO2) and undoped TiO2 particles. A 20% improvement in photocatalytic activity of reference TiO2 powder (powder ball milled without dopant addition) was achieved by B and Zr co-doping. The enhanced photocatalytic activity is attributed to synergistic effects of B-Zr co-doping the lattice of TiO2 as well as particle size reduction.

The present work reports a study of the effects of the compositions, and various catalytic additives and nanostructuring by high-energy ball milling, on the hydrogen storage properties of LiBH4, NaBH4, LiNH2 and LiAlH4 complex hydrides and their composites. The composites of (NaBH4+2Mg(OH)2) and (LiBH4+2Mg(OH)2) without and with nanometric nickel (n-Ni) added as a potential catalyst were synthesized by ball milling. The effect of the addition of 5 wt.% nanometric Ni on the dehydrogenation behavior of both the NaBH4-and LiBH4-based composites is rather negligible. In the (LiNH2+nMgH2) system, the phase transformations occurring as a function of the ball milling energy injected into the hydride system (LiNH2+nMgH2), having molar ratios n=0.5 to 2.0, have been thoroughly studied. The milling energy is estimated by a semi-empirical method. The results show that for the molar ratios n<1.0 three new phases such as LiH, amorphous Mg(NH2)2 (a-Mg(NH2)2) and Li2Mg(NH)2 are formed during ball milling depending on the injected energy. For the molar ratios n≥1.0 the new phase of MgNH forms whose formation is accompanied by a profound release of hydrogen. Addition of 5 %wt. KH can improve desorption rate of the LiNH2+0.5 MgH2 system. Furthermore this hydride system can be nearly fully rehydrogenated at 200°C and 50 bar H2 pressure. LiAlH4 containing 5 wt.% of nanometric Fe and Ni shows a profound mechanical dehydrogenation by continuously desorbing hydrogen (H2) during ball milling. X-ray diffraction studies show that Fe and Ni ions dissolve in the lattice, replacing the Al ions and forming a substitutional solid solution. Both Fe and Ni decrease the activation energies of stage I and II , but stage I is more sensitive to the particle size . The addition of 5 wt.% nano-size “interstitial compound” (n-TiC, n-TiN and n-ZrC) shows a continuous desorption of H2 is observed during high energy milling. Mechanical dehydrogenation rate of the doped samples increases noticeably during high-energy ball milling in the order of TiN > TiC > ZrC. The interstitial compound additives are able to strongly reduce the activation energy of Stage II dehydrogenation but do not substantially affect the apparent activation energy of Stage I .

Silver (Ag) was loaded to three different kinds (P-25, NT-22, and TiO(OH)2) of titanium dioxide (TiO2) powders through adding three different quantities (4.6, 9.2, and 13.8 ml) of silver nitrate (AgNO3) solution by mechanical ball milling process. X-Ray diffraction analysis suggested that Ag was loaded on the TiO2 powders in the form of silver oxide (AgO). SEM, particle size, and BET surface area analyses revealed that TiO2 particles agglomerated after ball milling, resulting in the decrease of specific surface area of the TiO2 powders. Powders P-25, NT-22, and TiO(OH)2 degraded 94 %, 46 %, and 26 %, respectively of MO solution under 1 h UV irradiation. Increasing amount of Ag loading enhanced photocatalytic activity of TiO2 powders under UV irradiation. The best photocatalytic performance was achieved by 13.8 ml AgNO3 solution added NT-22 powders. Percent methyl orange (MO) degradation of 13.8 ml AgNO3 solution added P-25, NT-22, and TiO(OH)2 powders under 1 h UV irradiation was 85 %, 96 %, and 67 %, respectively. Contact angle measurements revealed that hydrophilic properties of TiO2 powders were also improved by Ag loading. Moreover, TiO2 powders gained antibacterial prospect after Ag addition. Ag loaded TiO2 powders could be used effectively for the applications requiring better photocatalytic activity and antibacterial effect.

The present work reports a study of the effects of the compositions, and various catalytic additives and nanostructuring by high-energy ball milling, on the hydrogen storage properties of LiBH4, NaBH4, LiNH2 and LiAlH4 complex hydrides and their composites. The composites of (NaBH4+2Mg(OH)2) and (LiBH4+2Mg(OH)2) without and with nanometric nickel (n-Ni) added as a potential catalyst were synthesized by ball milling. The effect of the addition of 5 wt.% nanometric Ni on the dehydrogenation behavior of both the NaBH4-and LiBH4-based composites is rather negligible. In the (LiNH2+nMgH2) system, the phase transformations occurring as a function of the ball milling energy injected into the hydride system (LiNH2+nMgH2), having molar ratios n=0.5 to 2.0, have been thoroughly studied. The milling energy is estimated by a semi-empirical method. The results show that for the molar ratios n<1.0 three new phases such as LiH, amorphous Mg(NH2)2 (a-Mg(NH2)2) and Li2Mg(NH)2 are formed during ball milling depending on the injected energy. For the molar ratios n≥1.0 the new phase of MgNH forms whose formation is accompanied by a profound release of hydrogen. Addition of 5 %wt. KH can improve desorption rate of the LiNH2+0.5 MgH2 system. Furthermore this hydride system can be nearly fully rehydrogenated at 200°C and 50 bar H2 pressure. LiAlH4 containing 5 wt.% of nanometric Fe and Ni shows a profound mechanical dehydrogenation by continuously desorbing hydrogen (H2) during ball milling. X-ray diffraction studies show that Fe and Ni ions dissolve in the lattice, replacing the Al ions and forming a substitutional solid solution. Both Fe and Ni decrease the activation energies of stage I and II , but stage I is more sensitive to the particle size . The addition of 5 wt.% nano-size “interstitial compound” (n-TiC, n-TiN and n-ZrC) shows a continuous desorption of H2 is observed during high energy milling. Mechanical dehydrogenation rate of the doped samples increases noticeably during high-energy ball milling in the order of TiN > TiC > ZrC. The interstitial compound additives are able to strongly reduce the activation energy of Stage II dehydrogenation but do not substantially affect the apparent activation energy of Stage I .