Anthony Torres

Increasing the working temperature range of ZrF4-BaF2-LaF3-AlF3-NaF glass through microgravity processing

Abstract. Fluorozirconate glasses, such as ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF), have the potential for optical transmission from 0.3 μm in the ultraviolet to 7 μm in the infrared regions. However, crystallites formed during the fiber-drawing process prevent this glass from achieving its desired transmission range. The temperature at which the glass can be drawn into a fiber is known as the working range, defined as (Tx-Tg), bounded by the glass transition temperature (Tg) and the crystallization temperature (Tx). In contrast to silica glasses, the working temperature range for ZBLAN glass is extremely narrow. Multiple ZBLAN samples were subjected to a heating and quenching test apparatus on the parabolic aircraft under a controlled μ-g and hyper-g environments and compared with 1-g ground tests. Optical microscopy examination elucidates that crystal growth in ZBLAN is suppressed and initiates at a later temperature when processed in a microgravity environment. Thus, the crystallization temperature, Tx, at which the crystals form has increased. The glass transition temperature, Tg, remains constant, as crystallization does not occur until approximately 360°C for this composition of ZBLAN. Therefore, the working temperature range for ZBLAN has been broadened.

Experimental and Analytical Techniques for Studying ZBLAN Crystallization in Microgravity

One of the promising new areas of materials research is in the field of microgravity. Microgravity experimentation enables new materials to be developed and traditional materials to be improved, which cannot be completed under terrestrial conditions. Recent experiments on ZBLAN (ZrF4–BaF2–LaF3–AlF3 –NaF) glass have shown that, when heated, there is a crystallization dependency on gravity. This crystallization dependency limits the optical transmissibility of this material, due to crystallites forming during the fiber drawing process. ZBLAN glass has the theoretical potential for optical transmission in the range of 0.3 –7 μm, which would facilitate much needed mid-infrared (IR) fiber technology. Past researchers have completed ZBLAN crystallizationmicrogravity experiments, with limited details on the experimental technique and analysis methods. This study demonstrates an alternative experimental technique for ZBLAN microgravity testing and postprocessing techniques that reveal crystallinity in the sample.

The development of a modified bi-axial composite test specimen

The significance of bi-axial testing is increasing with the use of composites in more complex applications and the advent of new manufacturing techniques (Ash and Welsh. Collection of Technical Papers - AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, 2004, vol. 2, pp.1402–1412). Existing failure theories have not been proven to be accurate for predicting failure for laminated composites and very limited test data are available for woven composites (Ash and Welsh. Collection of Technical Papers – AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, 2004, vol 2, pp.1402–1412). It is believed that the fabrication process used to make composite bi-axial specimens induces initial damage into the specimen (Smits. Exp Anal Nano Eng Mater Struct 2007; 35: 933–934). Two different methods were developed to reduce the amount of damage induced into a bi-axial tests specimen. In addition, the effect of stress concentration due to a center hole added to a composite bi-axial specimen is studied.

Characterization of CRM Binders with Wax Additives Using an Atomic Force Microscopy (AFM) and an Optical Microscopy

This paper investigates the change in micromorphology of two binders and their respective warm mix asphalt binders before and after aging using atomic force microscopy (AFM) and optical microscopy. The control (PG 64-22) and crumb rubber modified (CRM) binders were blended with two different types of wax additives (L, a wax-based composition including crystal controller, and S, a long chain aliphatic hydrocarbon) and then artificially short-term and long-term aged using the rolling thin film oven and pressure aging vessel procedures. L is a wax based composition including crystal controller and S is a long chain aliphatic hydrocarbon. The AFM tapping-mode imaging technique was used to analyze the microstructure and the Superpave asphalt binder test was used to measure the rheology properties. In general, the results of this study indicated that (1) a correlation was observed between the changes in micromorphology (the distribution of dispersed domains and matrix) and rheology properties regardless of the aging, binder, and wax types; (2) the addition of crumb rubber into the base binder decreased the dimension of the catana phase (“bee-like”) structure, which increased the quantity of these structures; (3) the opposite trend was found between the aged control binder and the aged CRM binder regarding the size of the bee-like structure; (4) the long-term aging seemed to have a significant effect on the microstructures of the warm control and CRM binders; and (5) the inclusion of S and L was observed to have a similar trend for both binder types in terms of increased size of the bee-like structure and no bee-like structure, respectively.

Enhanced processability of ZrF4-BaF2-LaF3-AlF3-NaF glass in microgravity

Fluorozirconate glasses, such as ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF), have the potential for optical transmission from 0.3 μm in the UV to 7 μm in the IR region. However, crystallites formed during the fiber drawing process prevent this glass from achieving its desired transmission range. The temperature at which the glass can be drawn into a fiber is known as the working range, defined as (Tx - Tg), bounded by the glass transition temperature (Tg) and the crystallization temperature (Tx). In contrast to silica glasses, the working temperature range for ZBLAN glass is extremely narrow. Multiple ZBLAN samples were subject to a heating and quenching test apparatus on the parabolic aircraft, under a controlled 0-g and hyper-g environment and compared with 1-g ground tests. The microgravity duration on board Zero-G Corporation parabolic aircraft is approximately 20 seconds and the hyper-g intervals are approximately 56 seconds. Optical microscopy examination elucidates crystal growth in ZBLAN is suppressed when processed in a microgravity environment. The crystallization temperature, Tx, at which crystals form increased, therefore, significantly broadening the working temperature range for ZBLAN.

Measuring the Impact of Using Daily Objectives to Provide Rapid Feedback in Construction Courses

ABSTRACT In order to develop a systematic way to determine when students would benefit from additional in-class examples, a prior study presented the case study of using daily learning objectives as a rapid feedback system. This study presents a measurement of the impact of using these daily objectives as a rapid feedback system for construction science courses. The five separate courses implementing the system cover a breadth of construction topics providing a thorough investigation of construction education and the impact of the daily objective rapid feedback approach. The courses investigated were Structural Analysis, Construction Estimating, Construction Project Management, Understanding the Concrete Construction System, and Industrial Management and Scheduling. The assessment tools used to determine the impact of the system include pre and post questionnaires, and student grades with a comparison to offerings of each course in which the daily objective system was not implemented. Within the questionnaires there were general questions probing an individual student’s learning preference and questions to determine if the students’ valued the daily objective format. Comparison of student performance indicated no statistically significant changes, although there are some positive trends. The most significant result is that the students overwhelmingly believe that the system is useful to them.

Implementing Project Based Learning Pedagogy in Concrete Industry Project Management

ABSTRACT The objective of this study was to carry out a mixed methods construction education study seeking to improve student learning. This study uses project-based learning (PrBL) and milestone deliverable pedagogy to teach a concrete industry project management course and compares the outcome to a control (non-PrBL) version of the same course. The intervention course was designed as a full semester learning experience for students. The students worked as project managers from start to finish constantly contributing to the completion of their team project. In the control scenario, delivered in Fall 2013, students were required to carry-out a traditional project due at the end of the semester. This study examines the impact of having the course project become the main learning mechanism and considers and measures the ways in which PrBL affects student performance. Pre and post questionnaires regarding self-perceptions of learning and skill development were administered and project and course grades were used to assess the impact of PrBL on the students’ performance. The questionnaires revealed a minimum increase of students’ perception of their understanding of 48%. The course grade comparison showed an average of 13% point increase in all student grades when the PrBL pedagogy was implemented.

The Effect of Microcrystals on ZrF4–BaF2–LaF3–AlF3–NaF Glass Fiber Fracture

The mechanical response of materials to an applied force is determined by the inherent microstructure properties of the material.Microcrystals formed during heating and fiber drawing represent inherent flaws, which play a strong role in the mechanical properties as well as the handling ability of optical waveguides, in particular ZBLAN (ZrF4–BaF2–LaF3–AlF3–NaF) fibers. The property of the fiber to flex and bend is useful for handling and positioning the fiber in a desired application. A series of ZBLAN fibers were bent to specific radii of curvature to determine the applied curvature at which fiber fracture occurs. The fibers were first subjected to a tailored temperature arrangement for a designated amount of time to induce varying amounts of crystal formation. The fiber failure was documented and photographed with the aid of optical microscopy and scanning electron microscopy. Fracture mechanics analysis was used to characterize the impact of crystal size on the failure of the ZBLAN fiber. The results of this assessment show the impact of thermal degradation on ZBLAN fibers as well as suggest an optimum fiber drawing take-up reel diameter.

An Alternate Test Method for the Void Content of Pervious Concrete

In recent years, pervious concrete has become an emerging material for healthier ground water recharge and superior control of high stormwater runoff. This is facilitated by the high void content of the material. The void content percentage is an important design variable, as it correlates permeability as well as the strength of the material. Therefore, an accurate quantification of the void content is needed. A recently developed ASTM standard (ASTM C1754/C1754M-12) presents a method for determining the density and void content of hardened pervious concrete; however, there are still some issues apparent with this standard. The main issue is that the standard does not consider the absorption of the aggregate or the paste, which could adversely affect the results. Other concerns include the buoyant force due to trapped air when submerging the specimens, the high drying temperature in drying method B, which causes cracking and renders the specimen unusable for other testing, and the lengthy time requirement. This study further articulated these issues and presented two alternative testing techniques, one novel technique (Torres method) and one modified ASTM C1754 test method that can be used to better determine the void content of pervious concrete. The Torres method developed in this study placed the pervious concrete specimen in saturated surface dry (SSD) condition prior to determining the void percentage, such that the absorbed water mass was removed from the calculation. Additionally, a modified ASTM C1754 was developed that also placed the specimens in an SSD condition while still using the water tank used in ASTM C1754. The results from both of the developed methods showed lower void percentages for the specimens tested than with the current ASTM C1754 (drying method A and B) standard. The results indicated that including the absorbed water mass into the calculation ultimately resulted in higher void percentages.

Characterization of a Heating and Quenching Apparatus for Microgravity Testing

Microgravity experimentation enables new materials to be developed and traditional materials to be improved, which can’t be completed under terrestrial conditions. Recent developments on Heavy Metal Fluoride Glasses (HMFG’s) have shown that, when heated, there is a crystallization dependency on gravity. HMFG’s have the potential for optical transmission from 0.3 μm in the UV to 7 μm in the IR region, enabling fiber optic applications such as fiber amplifiers, radiometry, and mid-IR laser technology for surgery, drilling and cutting. The problem of devitrification from heat processing prevents this material from achieving its theoretical transmission range. Past researchers have shown that crystallization of HMFG’s is suppressed in microgravity and enhanced in hyper-gravity, however further investigation is still needed for a determination of this phenomenon. In this study, a HMFG heating and quenching testing apparatus was characterized and developed for microgravity and hyper-gravity testing. The testing apparatus was developed and characterized for use on a parabolic aircraft that provides a microgravity and hyper-gravity environment for experimental testing. The apparatus was successful in processing HMFG’s, which produced crystalline and non-crystalline glasses for future studies.