Finanzas Públicas Locales: El Déficit Público Provocado por Problemas de Recaudación en el Municipio de Tepetlaoxtoc, Estado de México

A lo largo de este proyecto indagatorio se atenderá el caso propio del municipio de Tepetlaoxtoc Estado de México, en donde se considerará la pregunta de investigación ¿Cómo lograr que la institución recaudadora de impuestos en el municipio de Tepetlaoxtoc haga una apropiada tarea para cumplir su propósito recaudador y de esta manera aumentar sus finanzas públicas para así dotar de servicios públicos a la población de manera integral y eficaz?Se estudia un caso particular en México en donde se prevé que las finanzas públicas se ven afectadas a causa de la inapropiada recaudación de impuestos y otras carencias administrativas, como lo es la falta de profesionalización de los servidores públicos, que crean una degeneración en el órgano recaudador de ingreso

Amorphous Al-Ti Powders Prepared by Mechanical Alloying and Consolidated by Electrical Resistance Sintering

A novel processing method for amorphous Al50Ti50 alloy, obtained by mechanical alloying and subsequently consolidated by electrical resistance sintering, has been investigated. The characterisation of the powders and the confirmation of the presence of amorphous phase have been carried out by laser diffraction, scanning electron microscopy, X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. The amorphous Al50Ti50 powders, milled for 75 h, have a high hardness and small plastic deformation capacity, not being possible to achieve green compacts for conventional sintering. Moreover, conventional sintering takes a long time, being not possible to avoid crystallisation. Amorphous powders have been consolidated by electrical resistance sintering. Electrically sintered compacts with different current intensities (7–8 kA) and processing times (0.8–1.6 s) show a porosity between 16.5 and 20%. The highest Vickers hardness of 662 HV is reached in the centre of an electrically sintered compact with 8 kA and 1.2 s from amorphous Al50Ti50 powder. The hardness results are compared with the values found in the literature.Ministerio de Economía y Competitividad (Spain) / Feder (EU) DPI2015-69550-C2-1-PMinisterio de Economía y Competitividad (Spain) / Feder (EU) DPI2015-69550-C2-2-

Medium-frequency electrical resistance sintering of oxidized C.P. iron powder

Commercially pure (C.P.) iron powders with a deliberate high degree of oxidation were consolidated by medium-frequency electrical resistance sintering (MF-ERS). This is a consolidation technique where pressure, and heat coming from a low-voltage and high-intensity electrical current, are simultaneously applied to a powder mass. In this work, the achieved densification rate is interpreted according to a qualitative microscopic model, based on the compacts global porosity and electrical resistance evolution. The effect of current intensity and sintering time on compacts was studied on the basis of micrographs revealing the porosity distribution inside the sintered compact. The microstructural characteristics of compacts consolidated by the traditional cold-press and furnace-sinter powder metallurgy route are compared with results of MF-ERS consolidation. The goodness of MF-ERS versus the problems of conventional sintering when working with oxidized powders is analyzed. The electrical consolidation can obtain higher densifications than the traditional route under non-reducing atmospheres.Ministerio de Economía y Competitividad DPI2015-69550-C2-1-PMinisterio de Economía y Competitividad DPI2015-69550-C2-2-

Electrical Resistivity of Powdered Porous Compacts

In this chapter, the problem of the electrical conduction in powdered systems is analyzed. New equations for computing the effective electrical resistivity of metallic powder aggregates and sintered compacts are proposed. In both cases, the effective electrical resistivity is a function of the bulk material resistivity, the sample porosity and the tap porosity of the starting powder. Additional parameters are required to describe the case of non-sintered powder aggregates: one of them describes a certain residual resistivity and another describes the rate of mechanical descaling during compression of the oxide layers covering the particles. Laws for the thermal dependence of these two parameters are also suggested. These new equations modeling the effective electrical resistivity are valid in all the physical range of porosity: from zero porosity to the tap porosity. Links between the proposed equations and the percolation conduction theory are stated. The proposed equations have been experimentally validated with powder aggregates (both in as-received state and after electrical activation to eliminate oxide layers) and sintered compacts of different metallic powders, resulting in a very good agreement with theoretical predictions. In addition to their general interest, the proposed models can be of great interest in modeling electrical consolidation techniques

Fabricación y caracterización de núcleos magnéticos de aleaciones amorfas mediante ruta pulvimetalúrgica simple y económica

La fabricación de núcleos amorfos (tanto para motores eléctricos, como transformadores) es una tarea compleja que hasta ahora ha requerido la fabricación del material amorfo en forma de cintas de fino espesor (mediante enfriamiento muy severo, melt spinning) y su posterior apilado y/o plegado para la formación de la pieza final. El proceso puede resultar costoso, y las propiedades de la pieza, a menudo, se resienten por el hecho de poseer demasiadas fronteras. Aunque se han ensayado diversos métodos para obtener materiales amorfos en bloque, ninguno, por el momento, está exento de dificultades y está explotándose industrialmente. El objeto de esta investigación es mostrar una ruta alternativa de fabricación de núcleos amorfos (o parcialmente nanocristalinos, embebidos en matriz amorfa), que permite obtener bloques de material (no formados por unión de cintas) con la forma definitiva, sustituyendo la técnica de melt spinning por una ruta pulvimetalúrgica consistente en la amorfización del polvo mediante molienda mecánica de alta energía y posterior consolidación rápida por vía eléctrica (técnicas FAST, abreviatura de Field Assisted Sintering Techniques). Esta combinación permite obtener piezas masivas de material amorfo (o parcialmente nanocristalino) con la forma definitiva.Manufacturing of amorphous cores (for electric motors and transformers) is a complex task that until now has required the manufacture of amorphous material in the form of thin strips (by very rapid cooling, melt spinning) and subsequent stacking and / or folded to form the final piece. The process can be expensive, and properties of the piece often resent to have too many borders. Although various methods have been tried for amorphous materials block, none, for the moment, is exempt from difficulties and is exploited industrially. The object of this research is to show an alternative route of manufacture of amorphous cores (or partially nanocrystalline, embedded in an amorphous matrix), giving material blocks (not formed by bonding tape) with the final form, replacing the technique of melt-spinning consisting of a powder amorphization by mechanical high energy milling and subsequent rapid consolidation by (FAST, Field Assisted Sintering Techniques) powder-metallurgical route. This combination allows to obtain massive pieces of amorphous material (or partially nanocrystalline) with the final form

Influence of Milling Atmosphere on the Controlled Formation of Ultrafine Dispersoids in Al-Based MMCs

Properties of compacts made from aluminium powder, milled under different atmospheres, were evaluated. The duration of all the milling processes was 10 h, although different atmospheres were tested: vacuum, confined ammonia, and vacuum combined with a short-time ammonia gas flow (5 min). Milled powders were consolidated by cold uniaxial pressing and vacuum sintering.The nature and content of the second phases change with the milling atmosphere, allowing the modification of the mechanical properties of the compacts. Results showed that hardness and tensile strength were highly dependent on the milling atmosphere. Milling carried out in vacuum with a short-time ammonia gas flow notably improved compacts’ properties, as compared with 10 h vacuum milling. Hardness increased from 96 to 150 HB, and ultimate tensile strength rose from 247 to 476 MPa.Ministerio de Economía y Competitividad DPI2015-69550-C2-1-P DPI2015-69550-C2-2-

Influence of processing parameters on the conduct of electrical resistance sintering of iron powders

The influence of the applied pressure and electrical parameters on the macrostructure of specimens consolidated by the medium-frequency electrical resistance sintering technique (MF-ERS) is analysed in this work. This technique is based on the application of pressure to a mass of conductive powder that, simultaneously, is being crossed by a high intensity and low voltage electric current. The simultaneous action of the pressure and the heat released by the Joule effect causes the densification and consolidation of the powder mass in a very short time. The effect of the current intensity and heating time on the global porosity, the porosity distribution, and the microhardness of sintered compacts is studied for two applied pressures (100 and 150 MPa). For the different experiments of electrical consolidation, a commercially available pure iron powder was chosen. For comparison purposes, the properties of the compacts consolidated by MF-ERS are compared with the results obtained by the conventional powder metallurgy route (cold pressing and furnace sintering). Results show that, as expected, higher current intensities and dwelling times, as well as higher pressures and the consolidation of compacts with lower aspects ratios, produce denser materials

Nanocrystalline Al Composites from Powder Milled under Ammonia Gas Flow

The production of high hardness and thermally stable nanocrystalline aluminium composites is described. Al powder was milled at room temperature in an ammonia flow for a period of less than 5 h. NH3 dissociation during milling provokes the absorption, at a high rate, of nitrogen into aluminium, hardening it by forming a solid solution. Controlled amounts of AlN and Al5O6N are formed during the subsequent sintering of milled powders for consolidation. The pinning action of these abundant dispersoids highly restrains aluminium grain growth during heating.The mean size of the Al grains remains below 45nm and even after the milled powder is sintered at 650∘C for 1h

Consolidation by MF-ERS of mechanically alloyed Al powder

The aim of this work is to study the viability of producing, by medium-frequency electrical resistance sintering (MF-ERS), compacts from mechanically alloyed aluminium powders. The MF-ERS process was carried out using different values of current intensity (6, 8, 10 and 11 kA) and dwelling (heating) times (400, 700 and 1000 ms). Results were compared with compacts processed by the conventional cold pressing and sintering route (850 MPa and 650 C-1h). Depending on the processing route different properties were obtained. The final porosity of the MF-ERS compacts (23.6e7%) can be as low, under the tougher tested sintering conditions, as that of the conventionally produced compacts (6%). The compacts obtained by MF-ERS are less ductile, with lower compression strength than that obtained by the conventional route. Furthermore, a similar electrical resistance and higher microhardness can be reached by the MF-ERS process, despite the duration of the consolidation process is only a fraction of that of the conventional process.Ministerio de Economía y Competitividad DPI2015-69550-C2-1-PFondo Europeo de Desarrollo Regional (FEDER) DPI2015-69550-C2-2-

A Method to Determine the Electrical Resistance of a Metallic Powder Mass under Compression

In this paper, a phenomenological model to predict the value of the electrical resistance of a compressed metal powder mass is proposed. The model, based on the experimental compressibility and resistivity-porosity curves, is useful in the field of the electrical resistance consolidation. In this area is often required to find out whether a certain mass of powder inside a die of specified inner section, and subjected to a certain compression, reaches a sufficiently small resistance value so that it can be consolidated by electrical means. The model also predicts the electrical resistance value of the powder mass in case of powders with no oxide layers, or after removing them mechanically or electrically by a previous activation process. The model predictions have been successfully validated through direct measurements of electrical resistance in powder aggregates both in as-received state and after electrical activation.Ministerio de Economía y Competitividad y Unión Europea DPI2015-69550-C2-1-P y DPI2015-69550-C2-2-