Micro-Drilling of ZTA and ATZ Ceramic Composit: Effect of Cutting Parameters on Surface Roughness

Ceramics are a class of materials widely used during last fifteen years for orthopaedic applications. It is well known that they are characterized by low wear rate, and friction coefficient. However, these materials are very difficult to machine into complex shapes because of their brittleness and high hardness. The most effective method to increase the crack resistance is the formation of a composite structure. This class of materials, composed by two or more different ceramics, can present higher characteristic respect to the single component, like fracture toughness and flexural strength. This paper presents a study of the influence of cutting parameters (cutting speed, feed rate and step number) onto the hole surface roughness and deformation due to the drill operation. The ceramic composite materials AZT (alumina toughened zirconia) and ZTA (zirconia toughened alumina) were first characterized in terms of hardness and roughness. After the drilling test, the holes were analyzed using scanning electron microscope (SEM) and an advanced 3-dimensional non-contact optical profilomete

The Church in Post-Transition Societies: Evidence From Eastern Europe.

I explore the relationship between religious affiliation and support for democratic values in postcommunist societies. Using the Tocquevillian idea of the institutional learning of democratic values within civil society, I examine three post-transition countries of Eastern Europe for evidence that the churches preserved and promoted democratic values during the years of Soviet regime control. Comparative historical examination of the relationship between the institutional churches and the state during the years of communist regime control demonstrate how the churches worked to preserve and promote democratic values. In those countries where the churches were marginalized and excluded from power by the state (such as Poland and East Germany) church elites worked to promote the reemergence of civil society. But where the churches were able to maintain a base of power through cooperation with the communist regime (Hungary) church elites were less involved in the democratic transformation process. Survey data on democratic attitudes in Poland, Hungary, and eastern Germany in the immediate post-transition period of 1990-1992 demonstrate that church attenders in these societies, similar to church attenders in western Germany, report higher levels of support for democratic values than non-attenders. Church attendance is strongly related to democratic values of confidence and trust in institutions, as well as support for a democratic form of government. Church attenders demonstrate more support for democratic values in societies where the church had an instrumental role in the recreation of civil society (Poland and eastern Germany) than they do in Hungary, where the church cooperated with the regime and did little to promote democratic values. Some evidence of optimism, trust, and efficacy among church attenders in these post-transition societies is also attributed to the church\u27s active participation in the transition

TAXONOMIC REVISION OF THE GENUS MANILKARA (SAPOTACEAE) IN MADAGASCAR

A revision of the five Madagascan species of the genus Manilkara (Sapotaceae) is presented, including a key, descriptions, diagnostic characters, ecological notes and a distribution map. Of the seven species originally described by Aubréville, Manilkara tampoloensis is placed in synonymy with M. boivinii, and M. sohihy is removed from the genus and placed within the existing Labramia boivinii (Pierre) Aubré

Rol de la concentración de Níquel en cátodos de óxidos Mn-Ni

Se estudió el comportamiento catódico de óxidos NixMn3 - xO4 (x=0,4; 0,5; 0,6; 0,7; 0,8) en medio ácido. Se muestra la influencia del níquel en la reactividad electroquímica de los cátodos. Los mejores resultados se obtienen con NiO,6Mn2,4O4 . La reactividad de los óxidos en la reducción catódica se explica a través de la concentración de los cationes en la estructura y de la ocurrencia del proceso redox entre Ni2+ y Mn3+ de los sitios octaédricos de la espinela

Inhibición de la corrosión de cobre en soluciones de ácido sulfúrico y cloruro de sodio mediante BTA y BIA

Se estudió el efecto del BTA y BIA en la corrosión del cobre en soluciones de ácido sulfúrico y cloruro de sodio a diferentes concentraciones de inhibidor. Se observó que el BT A es un eficiente inhibidor de la corrosión entre pH 1 a 4 y en medio salino. La concentración que ofrece buenas cualidades pasivantes es 1 • 10-3 M. Se postula que la acción del inhibidor es por adsorción física

Aspectos de la corrosión atmosférica de aceros autopasivables

Se estudia la corrosión de aceros Corten y Corcap en un medio que representa una atmósfera urbana industrial. Se compara el comportamiento frente a un acero al carbono corriente. La pasivación de los aceros especiales se logra mediante un ensayo acelerado de inmersiones y emersiones alternadas, la velocidad de corrosión instantánea se mide mediante técnicas electroquímicas de resistencia de polarización. Se discute el efecto que tiene un tratamiento térmico sobre el comportamiento a la corrosión. la capa de pasivaciónse determina mediante espectroscopia infrarroja y Mössbauer