2014 Temperature dependence of electrical conductivity has been studied for hot pressed AlN ceramic having different volume percentage of porosity (0.2 to 15 %) in the temperature range (500 K to 950 K). It has been observed that electrical conductivity decreases by two orders of magnitude as the volume percentage of porosity increases from 0.2 to 15 %. The effect of moisture on electrical cond...

We studied the mechanism of volatile-induced surface porosity formation during the resin transfer molding (RTM) of aerospace composites using a blended benzoxazine/epoxy resin, and identified reduction strategies based on material and processing parameters. The influence of viscosity and pressure on resin volatilization were determined. Then, in situ data was collected during molding using a la...

We model the formation of lunar complex craters and investigate the effect of preimpact porosity on their gravity signatures. We find that while preimpact target porosities less than ~7% produce negative residual Bouguer anomalies (BAs), porosities greater than ~7% produce positive anomalies whose magnitude is greater for impacted surfaces with higher initial porosity. Negative anomalies result...

Dealing with several structures of different complexities, we adopt various strategies to extract information. The general idea is to find appropriate tools to analyze the variation of the corresponding autocorrelation functions. First, for homogeneous media under different conditions, we recover, in a statistical way, a relationship between porosity and the autocorrelation function. Then, for ...

In this paper nuclear techniques were used to describe the structural characteristics of ceramic samples. These samples were produced mainly with silica to simulate sandstones. Three sets of samples with different characteristics were analyzed using gamma ray transmission to obtain point by point porosity and X-ray microtomography to obtain the porosity, for 2D sections and the scanned bulk, as...

-In this paper a three-phase model (liquid, solid and gas) of the mushy zone for investigation of porosity formation in solidifying castings is developed. This model takes into account the release of the dissolved gas from the alloy as well as heat transfer and interdendritic fluid flow in the mushy zone. An important aspect of this work is related to accounting for the term describing porosity...

OBJECTIVE To illustrate problems observed with low-porosity expanded polytetrafluoroethylene soft tissue implants and to describe a new dual-porosity implant, the technique for insertion, and this author's preliminary experience. METHOD A review of 175 pieces of SoftForm (Collagen Corporation, Palo Alto, Calif) placed in 69 patients over 3 years was performed. Between October 1, 1997, and Sep...

Zeolites are important materials whose utility in industry depends on the nature of their porous structure. Control over microporosity is therefore a vitally important target. Unfortunately, traditional methods for controlling porosity, in particular the use of organic structure-directing agents, are relatively coarse and provide almost no opportunity to tune the porosity as required. Here we s...

Porosity is a major problem occurring in aluminium alloy casting. During the process of solidification, alloy would shrink and emit dissolving hydrogen causing porosity formation inside the solidified part which leads to mechanical properties degradation. This research aims to produce a formula to explain the resulting porosity with the initial chemical compositions and cooling rate. A mathemat...

The porosity content in composite material is known to innuence the strength of the material. It is therefore of interest to monitor the porosity contents during manufacturing. Since attenuation and porosity are related, traditional porosity determination in composites is performed as attenuation measurements using ul-trasonic tone burst through-transmission. In this paper we propose a multivar...