Volume Dilatometry Research Articles

Specific Volume and Features of Compaction in Molding of Powder–Polymer Mixtures with Wax–Polypropylene Binder

This paper considers one of the current trends in powder metallurgy, the technology of forming powder–polymer mixtures by injection molding. For a powder–polymer mixture (feedstock) with a wax–polypropylene binder of the solution-thermal type of removal, the dependence of the PVT state parameters was studied by volume dilatometry. For each component of the polymer binder, the dependence of the phase transition temperature on pressure was determined. As a result of processing and analysis of PVT data for the feedstock of the type under study, we proposed a technological window of parameters that allow for injection molding of composite semifinished products with minimal volume shrinkage. Comparative analysis of the compactibility of feedstocks with a polymer binder of the catalytic and solution-thermal types of removal is carried out.

Magnetoelastic coupling in URu2Si2 : Probing multipolar correlations in the hidden order state

Time-reversal symmetry and magnetoelastic correlations are probed by means of high-resolution volume dilatometry in ${\mathrm{URu}}_{2}{\mathrm{Si}}_{2}$ at cryogenic temperatures, and magnetic fields sufficient to suppress the hidden order state at ${H}_{\mathrm{HO}}(T=0.66\phantom{\rule{0.28em}{0ex}}\mathrm{K})\ensuremath{\simeq}35$ T. We report a significant magnetoelastic volume expansion at and above ${H}_{\mathrm{HO}}(T)$, and even above ${T}_{\mathrm{HO}}$, possibly a consequence of field-induced $f$-electron localization. We investigate in detail the magnetostriction and magnetization as the temperature is reduced across two decades in temperature from 30 K where the system is paramagnetic, to 0.5 K in the realm of the hidden order state. We find a dominant quadratic-in-field dependence $\mathrm{\ensuremath{\Delta}}L/L\ensuremath{\propto}{H}^{2}$, a result consistent with a state that is symmetric under time reversal. The data shows, however, an incipient yet unmistakable asymptotic approach to linear ($\mathrm{\ensuremath{\Delta}}L/L\ensuremath{\propto}1\ensuremath{-}H/{H}_{0}$) for $15\phantom{\rule{4.pt}{0ex}}\text{T}<H<{H}_{\mathrm{HO}}(0.66\phantom{\rule{4.pt}{0ex}}\text{K})\ensuremath{\sim}40$ T at the lowest temperatures. We discuss these results in the framework of a Ginzburg-Landau formalism that proposes a complex order parameter for the HO phase to model the $(H,T,p)$ phase diagram.

Удельный объём и особенности уплотнения при формовании порошок-полимерных смесей с воск-полипропиленовым связующим

The article discusses one of the modern areas of powder metallurgy – the technology of manufacturing shaped parts by the powder injection molding (PIM). For the powder-polymer mixture (feedstock) with a wax-polypropylene binder of the solvent-thermal type of removal by isobaric volume dilatometry, the dependence of PVT state parameters was studied. For each component of the polymer binder, the dependence of pressure on the temperature of phase transition was obtained. As a result of mathematical processing and analysis of PVT data for the feedstock of the studied type, a technological window of parameters has been determined that allows injection molding of «green parts» with minimal volume shrinkage. The results of a comparative analysis of the compaction of feedstock with a polymer binder catalytic and solution-thermal type of removal are presented.

Photo-calorimetry method optimization for the study of light-initiated radical polymerization of dental resins

The properties of the dental resin composites have been studied extensively with several different methods including infrared and Raman spectroscopy, volume dilatometry, and mechanical analyses. Photo-calorimetry has also been used to measure the kinetics and extent of polymerization, but many of the variables associated with this technique remain to be fully defined and tested to enable quick and reproducible measurements under clinically relevant conditions. We have systematically varied the sample mass, light intensity, temperature, nitrogen purge time, and examined their effects on the monomer conversion and polymerization kinetics with the aim to optimize and standardize the photo-DSC method for the study of dental resins. A post-cure isothermal baseline at 37 °C yielded reproducible results. This systematic study detailing the effects of several variables of photo-calorimetry allows its direct use as a standard method to study polymerization kinetics and monomer conversion of dental resins and other photo-curable materials.

A Device to Measure the Shrinkage and Heat Transfers during the Curing Cycle of Thermoset Composites

Residual stresses development during manufacturing of composites depends mostly on the shrinkage behaviour of the polymer matrix from the point where stresses cannot be relaxed anymore. The matrix shrinkage may have a thermal and/or chemical origin and can leads to dimensional instability, ply cracking, delamination and fibre buckling. The approaches for measuring cure shrinkage can be classified as volume and non-volume dilatometry. Each technique has corresponding advantages and drawbacks but volume dilatometry is the one that is mostly used. In the present article, we report a home-built apparatus, named PVT-a mould, on which temperature, volume change and reaction conversion degree are measured simultaneously for an applied pressure. It can also be used to study the composite during curing and for the bulk samples having several millimetre thicknesses. The instrument is preferred over other techniques as it works in conditions close to the industrial ones. This device was used to measure cure shrinkage of resin and thermoset composite material with different fibre fractions as a function of temperature and reaction conversion degree. The heat of cure of the resin measured by PVT-a mould was compared to the results obtained by DSC.

Synthesis of shrinkage-controlled acrylic copolymers

Acrylic copolymer systems consisting of methyl methacrylate and triethylene glycol dimethacrylate with different chemical compositions were synthesized through bulk polymerization using N,N-dimethyl-p-toluidine as an acelerator to obtain nonshrinkable polymers. The use of the tertiary amine on this formulation produces an increase on the volume of the material due to a phase separation in the copolymer, which compensates the volume reduction upon curing. The specific volumes of all materials were determined by volume dilatometry using a dilatometer specially constructed for this purpose. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 586–591, 2000

Thermodynamic state, temperature transitions, and broadband dielectric relaxation behavior in gradient interpenetrating polymer networks

Traditional and gradient interpenetrating polymer networks (IPNs) of various composition have been prepared on the basis of crosslinked siliceous polyurethane and a copolymer of butylmethacrylate and dimethacrylate triethylene glycol. For various layers of gradient IPNs cut from the surface to the center of the sample detailed investigations by methods of volume dilatometry, vapor sorption and broadband ac dielectric relaxation spectroscopy were carried out. From data of benzene vapor sorption by various layers of gradient IPN the free energy of mixing of the IPN components has been calculated. For all the layers the free energies of mixing are positive and depend on the distance from the sample surface. Each layer consists of two phases with their own transition temperatures. From these data the composition of each phase for various layers has been calculated. The dipolar α mechanism of the polyurethane-rich phase and the ac conductivity mechanism were studied in detail by analyzing the dielectric susceptibility data within the complex permittivity and the modulus formalism. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:161–171, 1998

Dimensional stability of thermosensitive gutta-percha

The expansion and shrinkage of four commercial brands of endodontic thermosensitive gutta-percha were evaluated. A modified volume dilatometry technique was used; the dilatometric system (DS) consisted of Pyrex glass capillary tubes and a specimen chamber. Each sample was weighed to 10(-4) mg, placed in the specimen chamber, and subjected to vacuum for 45 min to eliminate moisture or gases. The DS was gradually heated from 24 degrees C to 80 degrees C and then cooled to 24 degrees C using a well-agitated temperature-controlled water bath. In a parallel set of experiments, the DS was heated in the same manner but cooled to body temperature (37 degrees C) in the water bath and the temperature kept stable at 37 degrees C for 24 h. The level of the mercury meniscus within the DS was monitored to determine the percent volume change of each sample at 2 degrees C intervals. All samples expanded as the temperature was elevated and shrank during cooling. The percent volume change for each of the four gutta-percha products, as the temperature was raised to 80 degrees C, ranged from an expansion of +11.62 to +12.25. As the temperature was lowered from 80 degrees C to 24 degrees C, the percent volume change representing shrinkage ranged from -2.22 to -3.53. When the temperature was lowered from 80 degrees C to 37 degrees C, the products continued to exhibit shrinkage for a range of time between 45 min and 10 h before stabilizing at a fixed volume. The final percent volume change for each experiment, with each product, was positive, ranging from +5.50 to +7.20, with discernible differences between products.

Effect of transcrystallinity on tensile behaviour of discontinuous carbon fibre reinforced semicrystalline thermoplastic composites

Short carbon fibre reinforced polyetheretherketone (PEEK) composites with and without transcrystalline interphase are prepared under different conditions, and are used to investigate the effect of transcrystalline interphase on the tensile behaviour of semicrystalline thermoplastic polymer based composites. Volume dilatometry and scanning electron microscopy (SEM) are also employed as supplementary means. It is found that the formation of transcrystalline interphase improves such important characteristics of the composites as tensile stiffness, strength and toughness. The transcrystalline interphase enhances fibre-matrix adhesion and reduces stress concentration and cavitation at the fibre ends. The predominant deformation mechanism of the composite is changed from cavitation to shearing process in the presence of transcrystalline interphase, and moreover, significant local plastic deformation that absorbs more energy occurs, resulting in cohesive failure of the composite instead of adhesive failure happening to the composite without transcrystalline interphase.

The origin of the β transition and its influence on physical ageing

Volume dilatometry was used to explore the origin of the β transition ( T β ) and its influence on physical ageing. The results show that volume recovery does occur even at temperatures below T β , a phenomenon indicating the existence of molecular rearrangements and cooperative motions below this point. Lowering the ageing temperatures through T β progressively retards short-term molecular rearrangements and cooperative motions. Nonetheless, the T β quench does not incur any excess free-volume trapping, and its associated change in specific volume follows a linear relationship with respect to temperature. The existence of T β is time-dependent, which leads to the conclusion that the formation of T β has a kinetic origin.

Glass and β transitions of atactic polystyrenes monitored by volume dilatometry

Abstract Volume recovery in the temperature range of above Tg to below T β has been studied for two atactic polystyrene specimens (M w = 210,000 and 300,000 g/mol). Observations clearly disclose the collapse of free volume even at temperatures well below Tβ. In an excess free volume sufficient environment, as the aging temperature is lowered through Tβ, the retardation of the initial volume recovery becomes progressively longer, forming a variation in the nonlinearity of the isotherms. Indeed, it is this variation that leads to the observation of the β transition in the V-T plot. The β transition is time dependent, but molecular weight independent. On the other hand, in addition to well-known molecular weight and time dependence, the glass transition has another important feature: The difference in thermal expansion coefficients above and below Tg increases slightly with aging time. Thus, time cannot alter the existence of Tg. Consequently, this study favors thermodynamic theories for the formation of Tg.

Changes in free volume and mechanical properties of PVC films incurred by quenching and aging

Abstract Using a specially constructed microbalance for hydrostatic weighing, the specific volume increase due to rapid quenching (∼500°C/sec) and the subsequent densification from physical aging have been observed for PVC thin films. The more severe the quench through its glass transition temperature (Tg), the greater is the free-volume content. Isobaric volume recovery at higher temperatures has further been investigated by volume dilatometry. Within the experimental time scale, aging of relaxing molecular rearrangements for PVC films takes place as a linear function of logarithmic aging time at temperatures far below Tg. When aging temperatures approach Tg, however, the isothermal volume contraction becomes nonlinear. The observed volumetric results follow the wellknown phenomena of physical aging. The changes in molecular mobility during quenching and aging have further been explored by means of tensile creep and stress-strain to failure. All results reflect that a relatively small change in free volu...

Structure and properties of thermoluminescent calcium fluoride glass-ceramic materials

New types of material for use inγ-dosimetry described here are glass-ceramics and silicate glass-ceramic enamels with thermoluminescent properties containing up to 30 wt% CaF2 doped with MnO2 and rare earth oxides. The structure and thermoluminescent properties of these materials have been investigated by applying a variety of complementary methods: X-ray analysis, electron microscopy, differential thermal analysis, electron paramagnetic resonance measurements and volume dilatometry. Thermal history, i.e. phase composition and degree of crystallinity, largely determines the thermoluminescent properties of the vitro-crystalline materials investigated. Optimal heat treatment favouring appropriate crystallization leads to a maximum in thermoluminescent intensity. Completely amorphous materials containing 20 to 30 wt% CaF2 in the form of a glassy solution are devoid of any thermoluminescence. The thermoluminescent properties of natural fluorite are compared with those of synthetic materials.

The physical aging of isotactic polypropylene

AbstractThe microstructural changes in isotactic polypropylene (PP), subsequent to quench from the melt to around Tg were studied using dynamic mechanical loss, volume dilatometry, small and wide angle X‐ray scattering, infrared and NMR spectroscopy. The β‐transition loss tangent and the specific volume decreased linearly with logarithm of aging time. Dynamic mechanical loss and NMR spectroscopy results established that amorphous chain mobility reduced during aging. X‐ray and IR techniques showed that the crystallinity, the crystalline density, and the average chain conformation do not change during aging. Tensile tests indicated that diffusion of air or moisture into the polymer is not a competitive mechanism for the aging phenomenon. A simple free‐volume model is quantitatively consistent with these observations. The fraction of the material which cannot age increased as the quench temperature decreased. Further, at lower temperatures a portion of the nonageable fraction is shown to reside in the amorphous fraction.

Some Observations on the Relationship Between Lubricant Mechanical and Dielectric Transitions Under Pressure

Viscoelastic transition measurements of several lubricants by volume dilatometry to pressures of 1.75 GPa, dielectric transitions at atmospheric pressure on five fluids in a frequency range of 0.2 to 500 kHz and on two fluids in the same frequency range to pressures of 0.55 GPa are reported. Lines of constant rate dilatometry transition, constant rate dielectric transition and constant viscosity are shown to be essentially parallel on a temperature-pressure diagram.

The time temperature position of the glass-rubber transition of amorphous polymers and the free volume

Accurate measurements of the shear creep compliance in the glass rubber transition region have been performed by means of a combined torsional pendulum and torsional creep apparatus over a broad experimental window for commercial PS, PMMA and PVC and for two slightly crosslinked rubbers, NR and PU. For the three plastic materials, specific volume vs. temperature curves were obtained by volume dilatometry under different rates of cooling.

Phase and relaxation transitions in polymers by the volume dilatometry method

Phase and relaxation transitions in polymers by the volume dilatometry method

Effect of tensile deformation on the melting point, specific volume, and volume coefficient of expansion of polyethylene

Disks of polyethylene of different density were subjected to plane tensile deformation along eight axes. It was established by volume dilatometry that the melting interval of the deformed plates had been shifted into the region of higher temperatures. It follows from the behavior of the specific volume increment associated with melting that deformation leads to the destruction of some of the low-melting structures and increases the content of higher-melting structures.

An enantiomorphic crystal—Crystal transition of trans-polybutadiene

The behaviour of trans-polybutadiene in an enantiomorphic crystal—crystal transition was measured by X-ray diffractometry and volume dilatometry. The crystal—crystal transition ranges lay between 33.1° and 43.3°C for the formation of a modification II as a decreasing I modification in the heating process, and between 36.5° and 26.3°C for the formation of a I modification as a decreasing II modification in the cooling process, as determined directly by taking X-ray diffraction diagrams of trans-polybutadiene. The specific volume/temperature curve of trans-polybutadiene shows a characteristic shape at the crystal—crystal transition ranges.

Polymerization and crosslinking characteristics of a 3‐methoxybutyl acrylate

AbstractPolymers of 3‐methoxybutyl acrylate (3‐MBA) were prepared by máss, solution, and emulsion polymerization techniques. The 3‐MBA polymers could be converted from soft, rubbery, soluble, thermoplastic films to hard, glossy, flexible, crosslinked films when exposed to air and/or transition metal catalysts at elevated temperatures. The crosslinked polymers are resistant to common organic solvents and to mineral acids. Strong alkalis degraded the crosslinked polymers. The second‐order transition temperature of poly‐3‐MBA is −56°C. as determined by volume dilatometry. A comparison of the crosslinking properties of poly‐3‐MBA and other alkyl and alkoxyalkyl polymers is discussed. An autoxidative mechanism is proposed for the crosslinking of 3‐MBA polymers.