Low TCE Polyimides from Polyamic Acid Blends and Copolymers: Preparation and Characterization Studies

1992 ◽  
Vol 264 ◽  
Author(s):  
Krishna G. Sachdev ◽  
Sandra Graham-Ode ◽  
Thomas L. Nunes ◽  
Paul S. Ho
Keyword(s):  
Experimental Data ◽  
Mechanical Properties ◽  
Residual Stress ◽  
Thermal Expansion ◽  
Silicon Wafers ◽  
Chain Segment ◽  
Flexible Chain ◽  
Polyamic Acid ◽  
Characterization Studies

AbstractA series of polyimides prepared from BPDA-PDA and BTDA-PDA polyamic acid blends and the corresponding (BPDA-PDA)x-(BTDA-PDA)y copolymers have been investigated for the mechanical properties, the thermal expansion, and the residual stress in films cured on silicon wafers. To determine the effect of inclusion of a highly flexible chain segment into BPDA-PDA structure, a BPDA-PDA/BDAF copolyimide has also been characterized. The experimental data are correlated with the chemistry and the composition of the blends and the copolyimides.

Waxd Study of Low TCE Polyimide Films Formed from Polyamic Acid Blends and Copolymers.

1992 ◽  
Vol 264 ◽  
Author(s):  
Thomas L. Nunes ◽  
Krishna G. Sachdev
Keyword(s):  
Molecular Structure ◽  
Tensile Strength ◽  
Crystallinity Index ◽  
Moisture Uptake ◽  
Chain Segment ◽  
Polyimide Films ◽  
Flexible Chain ◽  
Polyamic Acid ◽  
Out Of Plane ◽  
Molecular Anisotropy

AbstractLow TCE polyimides, typically BPDA-PDA and related materials are well known for their special properties which include low in-plane TCE, up to 3X higher elastic modulus and ultimate tensile strength, and lower moisture uptake relative to the commonly known flexible chain polyimides [1]. These differences are due to the rod-like orientation and highly organized molecular structure of the polyimides that are derived from linear-planar precursors resulting in more anisotropic properties such as the X-Y vs Z-direction TCE [2], and optical as well as dielectric properties.In the present study, we have measured the WAXD patterns of polyimide films formed from BPDA-PDA and BTDA-PDA polyamic acid mixtures and BPDA-BTDA-PDA random copolyamic acids. In order to examine the effect of a highly flexible chain segment on the molecular anisotropy of rod-like polyimides, preliminary WAXD patterns were recorded for films of BPDA-BDAF and a BPDA-PDA-BDAF copolyimide.An in-plane and an out-of-plane crystallinity index, measures of molecular order within the polyimide films studied were estimated from the WAXD patterns. The data are correlated with the various blends and copolymer compositions and discussed in terms of structural implications.

Measuring the elastic modulus and residual stress of freestanding thin films using nanoindentation techniques

2009 ◽  
Vol 24 (9) ◽  
pp. 2974-2985 ◽  
Author(s):  
Erik G. Herbert ◽  
Warren C. Oliver ◽  
Maarten P. de Boer ◽  
George M. Pharr
Keyword(s):  
Thin Films ◽  
Mechanical Properties ◽  
Residual Stress ◽  
Thermal Expansion ◽  
Elastic Modulus ◽  
Dimensional Analysis ◽  
Experimental Verification ◽  
Cu Films ◽  
Proposed Model ◽  
The Difference

A new method is proposed to determine the elastic modulus and residual stress of freestanding thin films based on nanoindentation techniques. The experimentally measured stiffness-displacement response is applied to a simple membrane model that assumes the film deformation is dominated by stretching as opposed to bending. Dimensional analysis is used to identify appropriate limitations of the proposed model. Experimental verification of the method is demonstrated for Al/0.5 wt% Cu films nominally 22 µm wide, 0.55 µm thick, and 150, 300, and 500 µm long. The estimated modulus for the four freestanding films match the value measured by electrostatic techniques to within 2%, and the residual stress to within 19.1%. The difference in residual stress can be completely accounted for by thermal expansion and a modest change in temperature of 3 °C. Numerous experimental pitfalls are identified and discussed. Collectively, these data and the technique used to generate them should help future investigators make more accurate and precise measurements of the mechanical properties of freestanding thin films using nanoindentation.

Analysis of Silicon Carbide and Silicon Nitride Precipitates in Block Cast Multicrystalline Silicon

2009 ◽  
Vol 156-158 ◽  
pp. 41-48 ◽  
Author(s):  
M. Holla ◽  
Tzanimir Arguirov ◽  
Winfried Seifert ◽  
Martin Kittler
Keyword(s):  
Mechanical Properties ◽  
Residual Stress ◽  
Raman Spectroscopy ◽  
Thermal Expansion ◽  
Electron Beam ◽  
Crystallization Process ◽  
Induced Current ◽  
Cathodoluminescence Spectroscopy ◽  
Electron Beam Induced Current ◽  
Optical And Mechanical Properties

We report on the optical and mechanical properties of Si3N4 inclusions, formed in the upper part of mc-Si blocks during the crystallization process. Those inclusions usually appear as crystalline hexagonal tubes or rods. Here we show that in many cases the Si3N4 inclusions contain crystalline Si in their core. The presence of the Si phase in the centre was proven by means of cathodoluminescence spectroscopy and imaging, electron beam induced current measurements and Raman spectroscopy. The crystalline Si3N4 phase was identified as β-Si3N4. Residual stress was revealed at the particles. While the stress is compressive in the Si material surrounding the Si3N4 particles tensile stress is found in the Si core. We assume that the stress is formed during cool down of the Si block and is a consequence of the larger thermal expansion coefficient of Si in comparison to that of β-Si3N4. Iron assisted nitridation of Si at temperatures below 1400 °C is considered a possible mechanism of Si3N4 formation.

Thermal Expansion Of GaN And Ain

1997 ◽  
Vol 482 ◽  
Author(s):  
Kai Wang ◽  
Robert R. Reeber
Keyword(s):  
Experimental Data ◽  
Residual Stress ◽  
Thermal Expansion ◽  
Lattice Parameter Data ◽  
Equations Of State ◽  
Lattice Parameter ◽  
Epitaxial Films ◽  
Residual Stress Distribution ◽  
Interatomic Potentials ◽  
Semiempirical Models

AbstractThe temperature dependence of the thermal expansion and the bulk modulus are critical for predicting the residual stress distribution in epitaxial films and provides information relevant for interatomic potentials and equations of state. The thermal expansions of aluminum nitride (AIN) and gallium nitride (GaN) are calculated with two models that employ the limited elastic and lattice parameter data. These semiempirical models allow prediction of the thermal expansions to higher temperatures. Calculated results are compared with experimental data.

Control of Residual Stress in Multilayered Alumina Composites Prepared Using EPD in a Strong Magnetic Field

2009 ◽  
Vol 412 ◽  
pp. 233-236 ◽  
Author(s):  
Tohru Suzuki ◽  
Tetsuo Uchikoshi ◽  
Yoshio Sakka
Keyword(s):  
Magnetic Field ◽  
Mechanical Properties ◽  
Residual Stress ◽  
Thermal Expansion ◽  
Strong Magnetic Field ◽  
The Other ◽  
Laminar Composites ◽  
Alumina Composites ◽  
The Difference ◽  
Oriented Layers

The mechanical properties of ceramics materials can be tailored by designing their microstructures. Residual stress is one of the important factors for controlling the crack propagation and consequently improving the mechanical properties. On the other hand, development of the crystallographic orientation even in a diamagnetic ceramic can be controlled by colloidal processing in a strong magnetic field. In this study, alumina/alumina laminar composites with different crystalline-oriented layers were fabricated by EPD in a strong magnetic field in order to control the residual stress using the difference in the thermal expansion of each layer.

Influence of aging on mechanical properties, wear and residual stress of a Heusler Al-Cu-Fe alloy

2019 ◽  
Vol 61 (1) ◽  
pp. 56-60 ◽  
Author(s):  
Fazil Husem ◽  
Fatma Meydaneri Tezel ◽  
Muhammet Emre Turan
Keyword(s):  
Mechanical Properties ◽  
Residual Stress

Residual stress and mechanical properties of polyimide thin films

2009 ◽  
Vol 113 (2) ◽  
pp. 976-983 ◽  
Author(s):  
Wonbong Jang ◽  
Jongchul Seo ◽  
Choonkeun Lee ◽  
Sang-Hyon Paek ◽  
Haksoo Han
Keyword(s):  
Thin Films ◽  
Mechanical Properties ◽  
Residual Stress

scholarly journals An Additive Model to Predict the Rheological and Mechanical Properties of Polypropylene Blends Made by Virgin and Reprocessed Components

Recycling ◽  
2021 ◽  
Vol 6 (1) ◽  
pp. 2
Author(s):  
Francesco Paolo La Mantia ◽  
Maria Chiara Mistretta ◽  
Vincenzo Titone
Keyword(s):  
Experimental Data ◽  
Mechanical Properties ◽  
Additive Model ◽  
Industrial Process ◽  
Theoretical Predictions ◽  
Experimental Values ◽  
Polypropylene Blends ◽  
Polypropylene Sample

In this work, an additive model for the prediction of the rheological and mechanical properties of monopolymer blends made by virgin and reprocessed components is proposed. A polypropylene sample has been reprocessed more times in an extruder and monopolymer blends have been prepared by simulating an industrial process. The scraps are exposed to regrinding and are melt reprocessed before mixing with the virgin polymer. The reprocessed polymer is, then, subjected to some thermomechanical degradation. Rheological and mechanical experimental data have been compared with the theoretical predictions. The results obtained showed that the values of this simple additive model are a very good fit for the experimental values of both rheological and mechanical properties.

Monitoring of mechanical properties of prestressed glass fiber epoxy composites over 12 months after fabrication

2021 ◽  
pp. 002199832110047
Author(s):  
Mahmoud Mohamed ◽  
Siddhartha Brahma ◽  
Haibin Ning ◽  
Selvum Pillay
Keyword(s):  
Mechanical Properties ◽  
Residual Stress ◽  
Flexural Strength ◽  
Compressive Residual Stress ◽  
Fiber Volume Fraction ◽  
Volume Fraction ◽  
Epoxy Composites ◽  
Flexural Properties ◽  
Initial Increase ◽  
Fiber Volume

Fiber prestressing during matrix curing can significantly improve the mechanical properties of fiber-reinforced polymer composites. One primary reason behind this improvement is the generated compressive residual stress within the cured matrix, which impedes cracks initiation and propagation. However, the prestressing force might diminish progressively with time due to the creep of the compressed matrix and the relaxation of the tensioned fiber. As a result, the initial compressive residual stress and the acquired improvement in mechanical properties are prone to decline over time. Therefore, it is necessary to evaluate the mechanical properties of the prestressed composites as time proceeds. This study monitors the change in the tensile and flexural properties of unidirectional prestressed glass fiber reinforced epoxy composites over a period of 12 months after manufacturing. The composites were prepared using three different fiber volume fractions 25%, 30%, and 40%. The results of mechanical testing showed that the prestressed composites acquired an initial increase up to 29% in the tensile properties and up to 32% in the flexural properties compared to the non-prestressed counterparts. Throughout the 12 months of study, the initial increase in both tensile and flexural strength showed a progressive reduction. The loss ratio of the initial increase was observed to be inversely proportional to the fiber volume fraction. For the prestressed composites fabricated with 25%, 30%, and 40% fiber volume fraction, the initial increase in tensile and flexural strength dropped by 29%, 25%, and 17%, respectively and by 34%, 26%, and 21%, respectively at the end of the study. Approximately 50% of the total loss took place over the first month after the manufacture, while after the sixth month, the reduction in mechanical properties became insignificant. Tensile modulus started to show a very slight reduction after the fourth/sixth month, while the flexural modulus reduction was observed from the beginning. Although the prestressed composites displayed time-dependent losses, their long-term mechanical properties still outperformed the non-prestressed counterparts.

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