The Dependence of Ultrasonic Velocity in Ultra-Low Expansion Glass on Temperature

The coefficient of thermal expansion (CTE) is an important property of ultra-low expansion (ULE) glass, and the ultrasonic velocity method has shown excellent performance for the nondestructive measurement of CTE in large ULE glass. In this method, the accurate acquisition of the ultrasonic velocity in ULE glass is necessary. Herein, we present a correlation method to determine the ultrasonic TOF in ULE glass and to further obtain the ultrasonic longitudinal wave velocity (cL) indirectly. The performance of this method was verified by simulations. Considering the dependence of cL on temperature (T), we carried out the derivation of the analytical model between cL and T. Based on reasonable constant assumptions in the physical sense, a cL–T exponential model was produced, and some experimental results support this model. Additional experiments were carried out to validate the accuracy of the cL–T exponential model. The studies we conducted indicate that the cL–T exponential model can reliably predict the ultrasonic velocity in ULE glass at different temperatures, providing a means for the nondestructive CTE measurement of large ULE glass at a specified temperature.

Evolution of Microstructure, Mechanical Properties and Residual Stress of a Cold Rolled Invar Sheet Due to Heat Treatment

Invar alloy possesses a uniquely low coefficient of thermal expansion, making it an ideal material for fine metal masks. To manufacture fine metal masks, Invar alloys are often cold-rolled, during which residual stress develops. Heat treatment is an effective means to control residual stress that develops within Invar sheets after cold rolling, but the treatment should be carried out with care. In this article, a comprehensive study on the effect of heat treatment on the residual stress, microstructure, and mechanical properties of a cold-rolled Invar sheet is reported. We show that while both recovery and recrystallization are effective means of reducing residual stress, substantial microstructural changes and, therefore, notable changes in mechanical properties and residual stress, occur after recrystallization. Moreover, residual stress release due to recrystallization can be affected by microstructure and texture prior to heat treatment as these factors play a significant role in recrystallization.

Thermal Properties of Copper Matrix-Ceramic Filler Composite Prepared by Polymer Solution Method

A copper (Cu) metal-ceramic filler composite with high thermal conductivity and a suitable thermal expansion coefficient was designed for application as a high-performance heat dissipation material. The purpose of the designed material was to utilize the high thermal conductivity of Cu while lowering its high coefficient of thermal expansion by using a ceramic filler. In this study, a Cu-sol containing a certain amount of AlN or SiC ceramic filler was prepared using a non-aqueous solvent. A complex was produced by applying a PVB polymer to prepare a homogeneous precursor. The composite sintered without pressure in a reducing atmosphere showed low thermal conductivity due to residual pores, but the hot press sintered composite exhibited improved thermal conductivity. The Cu composite with 30 wt% AlN filler added exhibited a thermal conductivity of 290 W/m·K and a thermal expansion coefficient of 9.2 × 10-6/oC. Due to the pores in the composite, the thermal conductivity showed some difference from the theoretical value calculated from the rule of mixture. However, the thermal expansion coefficient did not show any significant difference.

Структурный переход и температурные зависимости коэффициентов теплового расширения NaNO-=SUB=-3-=/SUB=-, внедренного в нанопористое стекло

The temperature evolution of the crystal structure of a nanocomposite material obtained by introducing sodium nitrate NaNO3 from a melt under pressure into a nanoporous alkali borosilicate glass with an average pore diameter of 7 nm has been studied by the method of diffraction of synchrotron radiation in a wide temperature range upon heating. Analysis of the experimental diffraction patterns revealed a significant decrease in the temperature of the structural (orientational) transition by more than 50 K (up to 496 K) compared to bulk sodium nitrate. From the temperature dependence of the intensity of the superstructure peak (113), the dependence of the critical exponent β (T) for this transition was obtained and a significant difference from the critical exponent for a bulk material was found in the temperature range from 455 K to the transition temperature. Analysis of the broadening of Bragg reflections made it possible to estimate the average size (~ 40 nm) of sodium nitrate nanoparticles into the pores. An increase in the linear coefficient of thermal expansion in the [001] direction was found in NaNO3 nanoparticles in comparison with bulk material at temperatures above 450 K.

Cryogenic thermal insulating and mechanical properties of rigid polyurethane foams blown with hydrofluoroolefin: Effect of perfluoroalkane

The effect of perfluoroalkane (PFA) on the morphology, thermal conductivity, mechanical properties and thermal stability of rigid polyurethane (PU) foams was investigated under ambient and cryogenic conditions. The PU foams were blown with hydrofluorolefin. Morphological results showed that the minimum cell size (153 μm) was observed when the PFA content was 1.0 part per hundred polyols by weight (php). This was due to the lower surface tension of the mixed polyol solution when the PFA content was 1.0 php. The thermal conductivity of PU foams measured under ambient (0.0215 W/mK) and cryogenic (0.0179 W/mK at −100°C) conditions reached a minimum when the PFA content was 1.0 php. The low value of thermal conductivity was a result of the small cell size of the foams. The above results suggest that PFA acted as a nucleating agent to enhanced the thermal insulation properties of PU foams. The compressive and shear strengths of the PU foams did not appreciably change with PFA content at either −170°C or 20°C. However, it shows that the mechanical strengths at −170°C and 20°C for the PU foams meet the specification. Coefficient of thermal expansion, and thermal shock tests of the PU foams showed enough thermal stability for the LNG carrier’s operation temperature. Therefore, it is suggested that the PU foams blown by HFO with the PFA addition can be used as a thermal insulation material for a conventional LNG carrier.

Effect of Accelerated Cooling on Linepipe Steel Mill Scale and Resulting Localized Corrosion Susceptibility

The structure and composition of mill scale on linepipe steel formed with and without accelerated cooling conditions (ACC) was investigated and correlated to localized corrosion susceptibility. The mill scale structure/composition was investigated using scanning electron microscopy equipped with X-ray energy dispersive spectroscopy and electron back scatter diffraction, as well as X-ray diffraction. Localized dissolution of the mill scale was investigated using electrochemical techniques including open circuit potential measurements, electrochemical impedance spectroscopy, and electrochemical noise measurements in a corrosive phase solution. The various surface analytical and electrochemical techniques indicated that the mill scale formed without ACC consists of a relatively crack-free, thick inner wüstite layer with a thinner magnetite outer layer. However, the mill scale formed with ACC comprised a magnetite layer containing islands of retained wüstite, with some evidence of magnetite/iron eutectoid formation and which exhibited a relatively high density of through-scale cracks. These cracks can provide direct paths that connect the corrosive solution to the steel substrate, leading to more rapid breakdown of the mill scale. Additionally, the cracks can form a crevice between the mill scale and the steel surface, providing sites for pit initiation and growth. Coefficient of thermal expansion mismatch thermal stress calculations indicate that a magnetite-based scale is more susceptible to cracking/spalling than a wüstite-based scale, resulting in the ACC plate being more susceptible to localized corrosion.

POLYMER COMPOSITE MATERIALS BASED ON POLYTETRAFLUOROETHYLENE FILLED WITH MODIFIED MONTMORILLONITE

Актуальность исследования состоит в том, что одними из перспективных конструкционных и функциональных материалов остаются полимерные композиты на основе политетрафторэтилена. Благодаря уникальным базовым свойствам он находит широкое применение во всех отраслях промышленности, прежде всего в качестве антифрикционных материалов для узлов трения. В условиях низких температур композиты на основе ПТФЭ являются наиболее перспективными триботехническими материалами для сохранения работоспособности техники и оборудования Севера и арктических регионов. Недостатком ПТФЭ являются низкая износостойкость, хладотекучесть, высокий коэффициент термического расширения, которые можно улучшить добавлением наполнителей.Целью работы является исследование влияния монтмориллонита марки Метамона®1Н1 на свойства и структуру политетрафторэтилена (ПТФЭ).В качестве полимерной матрицы использован политетрафторэтилен марки ПТФЭ марки ПН-90, ООО «Галополимер»,г. Пермь.В качестве наполнителя использован Монтмориллонит марки МЕТАМОН® 1Н1 – гидрофильная глина, представляющая очищенный природный Na+ - монтмориллонит.Введение активированного метамона в композиты позволяет повысить деформационно-прочностные характеристики ПКМ по сравнению с исходным ПТФЭ.В данной работе представлены результаты исследований влияния органомодифицированного механоактивированного монтмориллонита (оММТ) марки 101/102 на физико-механические характеристики и структуру политетрафторэтилена. Содержание наполнителя варьировали от 0,5 до 7 мас. %. Установлено, что при введении 0,1-5,0 мас. % оММТ в ПТФЭ прочность ПКМ увеличивается на 25 %, относительное удлинение на 21%. Структурными исследованиями зарегистрирована трансформация надмолекулярной структуры ПТФЭ с формированием сферолитоподобных образований, центрами кристаллизации которых являются частицы оММТ. Для этих концентраций наполнителя установлены более высокие показатели энтальпии плавления и степени кристалличности методом дифференциальной сканирующей калориметрии. The development of modern technology requires the search for new structural materials that surpass traditional ones in their deformation-strength, elastic and wear-resistant properties. Composite materials based on PTFE are very promising structural materials for many industries.PTFE is widely used in friction units of technical systems due to its operability in a wide temperature range while maintaining low and stable values of the coefficient of friction, as well as its ability to provide self-lubrication during friction. Such disadvantages of PTFE as cold flow, low wear resistance, high coefficient of thermal expansion are eliminated by modification, one of the common methods of which is filling.The paper focuses on the effect of organomodified mechanically activated montmorillonite (OMMT) of 101/102 grade on the physical and mechanical characteristics and structure of polytetrafluoroethylene. The filler content varied from 0.5 to 7 wt. %. With the introduction of 0.1-5.0 wt. % OMMT in PTFE, the strength of PCM increases by 35%, and the elongation by 21% was found. Structural studies have registered the transformation of the supramolecular structure of PTFE with the formation of spherulite-like formations, the centers of crystallization of which are particles of OMMT. For these filler concentrations, higher values ​​of the enthalpy of melting and the degree of crystallinity were established by the method of differential scanning calorimetry.

Thermal Fringe Formation During a Hologram Recording Using a Dry Photopolymer

In this study we investigated the undesired but possible fringe formation during the recording of large size holographic optical elements (HOE) using a dry photopolymer. We identified the deformation of the recording element during hologram exposure as the main source for this fringe formation. This deformation is caused mainly by the one-sided heating of the recording element, namely, the dry photopolymer–recording plate stack. It turned out that the main source for this heating was the heat of polymerization in the dry photopolymer released during the exposure interval. These insights were translated into a physical model with which quantitative predictions about thermal fringe formation can be made depending on the actual HOE recording geometry, recording conditions and characteristics of the dry photopolymer. Using this model, different types of large size HOEs, used as components to generate a steerable confined view box for a 23” diagonal size display demonstrator, could be recorded successfully without thermal fringe formation. Key strategies to avoid thermal fringe formation deduced from this model include balancing the ratio of lateral recording plate dimension R to its thickness h, recording the power density P or equivalently the exposure time texp at a fixed recording dosage E, and most importantly recording the the linear coefficient of thermal expansion (CTE) of the recording plate material. Suitable glass plates with extremely low CTE were identified and used for recording of the above-mentioned HOEs.