Showing papers on "Devitrification published in 2015"

Development of interatomic potentials appropriate for simulation of devitrification of Al90Sm10 alloy

Abstract: In this study, a semi-empirical potential for the Al90Sm10 alloy is presented. The potential provides satisfactory reproduction of pure Al properties, the formation energies of a set of Al–Sm crystal phases with Sm content about 10%, and the structure of the liquid Al90Sm10 alloy. During molecular dynamics simulation in which the liquid alloy is cooled at a rate of 1010 K/s, the developed potential produces a glass structure with lower ab initio energy than that produced by ab initio molecular dynamics (AIMD) itself using a typical AIMD cooling rate of 8 ∙1013 K/s. Based on these facts the developed potential should be suitable for simulations of phase transformations in the Al90Sm10 alloy.

Preserved glass-rich impactites on Mars

Abstract: Quenched glass formed by hypervelocity impacts can encapsulate and preserve biosignatures on Earth, demonstrating the fossilization potential of glass-rich impactites on Mars. However, definitive spectral signatures of impact glass have not been identified on the martian surface from orbital remote sensing. Here we present a remote compositional survey of probable impactites in well-preserved craters, using data from the Compact Reconnaissance Imaging Spectrometer for Mars. These units are composed of mafic glasses mixed with crystalline phases including olivine and pyroxene, determined by radiative transfer Hapke modeling followed by spectral mixture analysis. This glassy material likely formed from impact-induced melting of the target rock with rapid quenching and minor subsequent devitrification or chemical alteration. The metastable glass has been preserved by the cold and dry martian climate during the Amazonian period, and this preservation—as confirmed here across the planet—provides a means to trap signs of ancient life on the accessible martian surface. Our results lend concrete support to theoretical arguments suggesting that impact glass has formed in abundance on Mars, both inside of craters and as spherules in distal strewnfields. Contrary to previous ideas, martian impact products are not destroyed by interaction with volatiles during the impact process.

Production and characterisation of granulated frit to achieve anorthite based glass–ceramic glaze

Abstract: For the development of matt-transparent glass–ceramic coating applied on the porcelain tile, the CaO–Al2O3–SiO2 system was studied. Sinterization and devitrification behavior of granulated frits and viscosity change with temperature were analyzed by combining the data that belong to differential thermal analysis and heating microscope analysis. Characterization by X-ray diffraction (XRD) combined with scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) microanalysis show that needle like crystals of anortite is formed. Crystal size of anorthite was adjusted by modifying composition. Since anorthite crystals cannot be made smaller than wavelength of light in the studied system, anorthite crystal size is increased to reduce light refraction so that light is homogeneously distributed. Anorthite crystals with low refractive index crystallized as rod-like crystals and distributed homogenously in the system. Thus, the light is allowed to pass through the substrate and as a conclusion transparent appearance of the glaze is increased.

Classical Bioglass® and innovative CaO-rich bioglass powders processed by Spark Plasma Sintering: A comparative study

Abstract: Densification and crystallization phenomena taking place when a recently developed CaO-rich bioactive glass and conventional 45S5 Bioglass ® are processed by Spark Plasma Sintering (SPS) are examined. Fully dense and wholly amorphous products can be obtained from the new glass composition at 730 °C after 2 min dwell time. Moreover, temperatures equal or higher than 830 °C are needed to induce crystallization (α- and β-CaSiO 3 ) in the parent glass. Conversely, Na 6 Ca 3 Si 6 O 18 crystals are formed in sintered 45S5 samples produced under optimal conditions (550 °C, 2 min), although the glassy character is still preserved. Products resulting from the innovative glass powders generally display higher hardness and local elastic modulus. Devitrification also provides improvements in this system. In contrast, mechanical properties become slightly worsen when classical bioglass is processed at 600 °C. This can be probably associated to the corresponding decrease in compactness which, apparently, overcomes the benefits arising from the crystallization progress.

Three-Phase Morphology of Semicrystalline Polymer Semiconductors: A Quantitative Analysis

Abstract: Quantitative morphological analysis is essential to the fundamental understanding of semiconducting polymers. Temperature modulated differential scanning calorimetry is used to determine the amount of crystalline and noncrystalline phases within regioregular poly(3-hexylthiophene) (rrP3HT). Careful optimization of the experimental conditions shows that the glass transition of rrP3HT consists of three parts corresponding to the devitrification of the side chains, mobile amorphous fraction (MAF), and rigid amorphous fraction (RAF), consecutively. Measurements taken from this, as well as from the melting transition, allows the first calculation of the degree of crystallinity, MAF and RAF, to be achieved in a single experiment for rrP3HT. This technique thus enables the morphological phases to be determined and potentially related to the performance of electronic devices made from semiconducting polymers.

Devitrification Properties of Vapor-Deposited Ethylcyclohexane Glasses and Interpretation of the Molecular Mechanism for Formation of Vapor-Deposited Glasses

Abstract: We constructed an adiabatic calorimeter adapted for the preparation and in situ thermal characterization of vapor-deposited glasses and reported the investigation of the enthalpic states and dynamic properties of ethylcyclohexane (ECH) glasses prepared by vapor deposition in the temperature range of (0.71–0.96)Tg,liq; Tg,liq = (101 ± 1) K is the calorimetric glass transition temperature of the bulk liquid. It was verified that the ECH glasses deposited at temperatures immediately below Tg,liq were characterized by lower enthalpies and higher devitrification temperatures (Tdev), as compared to the glass obtained by supercooling the bulk liquid. The deposition temperature (TD) expected to yield experimentally the entity with the highest Tdev and the lowest enthalpic state was estimated to be 0.93Tg,liq. A model potentially elucidating the fundamental mechanism of formation and devitrification for the glasses prepared via the physical vapor deposition method as a function of TD was proposed. The fundamental ...

Glass for chemical strengthening, chemically strengthened glass, and method for producing chemically strengthened glass

Abstract: An object of the present invention is to provide a glass for chemical strengthening which is capable of improving strength as compared with an ordinary soda lime silicate glass even when the same chemical strengthening treatment as that in a conventional process is applied and has good devitrification characteristics, a chemically strengthened glass using the glass for chemical strengthening, and a method for producing the chemically strengthened glass. The present invention provides a glass for chemical strengthening having a specific glass composition described in the present specification.

Kinetics and Mechanisms of Isothermal Devitrification in Amorphous Cu 50 Zr 50

Abstract: The crystallization kinetics and microstructural dynamics associated with devitrifying a melt-spun Cu50Zr50 metallic glass were investigated using isothermal treatments, in situ high-energy synchrotron X-ray diffraction, conventional and high-resolution transmission electron microscopy, and differential scanning calorimetry. The analysis of isothermal transformations allows us to more clearly unravel the complex interplay between nucleation and growth of competing stable and metastable phases. The isothermal devitrification response was found to involve the Cu10Zr7, CuZr2, and CuZr phases, consistent with previously reported constant heating rate experiments, but here we have resolved the phase evolution and structural characteristics of the transformation, including the very early stages of crystallization. At 671 K (398 °C), the isothermal transformation starts with the formation of the Cu10Zr7 phase, which grows in a generally equiaxed morphology. At a size of approximately 100 nm, the growth of the Cu10Zr7 particles is interrupted by the precipitation of a thin layer of the CuZr2 phase, upon which the metastable CuZr (B2) grows epitaxially. Crystallization kinetics are quantified here though in situ measurements (HEXRD, DSC) and ex situ microstructural analysis (TEM, HRTEM). Finally, the influences of chemical partitioning, diffusion, and crystallographic orientation on this sequence are examined.

Unconventional phase selection in high-driven systems: A complex metastable structure prevails over simple stable phases

Abstract: Phase selection in deeply undercooled liquids and devitrified glasses during heating involves complex interplay between the barriers to nucleation and the ability for these nuclei to grow. During the devitrification of glassy alloys, complicated metastable structures often precipitate instead of simpler, more stable compounds. Here, we access this unconventional type of phase selections by investigating an Al-10%Sm system, where a complicated cubic structure first precipitates with a large lattice parameter of 1.4 nm. We not only solve the structure of this "big cubic" phase containing ~140 atoms but establish an explicit interconnection between the structural orderings of the amorphous alloy and the cubic phase, which provides a low-barrier nucleation pathway at low temperatures. The surprising rapid growth of the crystal is attributed to its high tolerance to point defects, which minimize the short-scale atomic rearrangements to form the crystal. Our study suggests a new scenario of devitrification, where phase transformation proceeds initially without partitioning through a complex intermediate crystal phase.

Glass-transition process in an Au-based metallic glass

Abstract: In the present paper, the glass-transition phenomenon in an Au-based metallic glass has been studied using a step-scan calorimetry measurement. The existence of two distinct slopes within the glass-transition region one starting at low temperature (about 340 K) and the other at higher temperature (about 380 K) likely indicates two glass-transition processes. This phenomenon is rather related to different diffusion coefficients of the alloying elements in this complex alloy in solid state. Structural relaxation of the glassy phase before reaching the glass-transition region also shows a complex behavior.

Influence of phosphate precursors on the structure, crystallization behaviour and bioactivity of sol–gel derived 45S5 bioglass

Abstract: Obtaining bioglass composition 45S5® in completely amorphous form without crystalline inclusion by the sol–gel route has remained a challenge so far. Here, we demonstrate that with appropriate phosphate precursor and by controlling the polymerization and gelation reactions by adjusting the pH of the reactants, one can overcome this challenge. As-synthesized glass was heat treated to understand the devitrification behaviour of the sol–gel derived glass and to obtain bioglass–ceramics. As-synthesized and heat treated glasses were characterized using powder X-ray diffraction, transmission electron microscope, differential scanning calorimeter and differential thermal analyzer. For assessing the in vitro bioactivity of sol–gel derived glass and glass–ceramic powders, we tested the apatite forming ability on their surface upon immersion in simulated body fluid. Properties of sol-derived 45S5 glass are then compared with the bulk counterpart obtained by conventional melt quenching method. This study reveals a procedure to prepare completely amorphous sol–gel derived 45S5 glass which can be used as a bioactive material for bone implant, tooth coating, bone tissue engineering and drug delivery applications.

Influence of niobium on laser de-vitrification of Fe–Si–B based amorphous magnetic alloys

Abstract: Laser annealing of Fe77.5Si13.5B9 and Fe76.5Si13.5B9Cu1 amorphous melt-spun ribbons was carried out. In both alloys, it was found that devitrification occurred, leading to the nucleation of a high density of refined α-Fe(Si) nanocrystals within the amorphous matrix. Interestingly, when laser processed under identical conditions, Fe74.5Si13.5B9Nb3, and Fe73.5Si13.5B9Nb3Cu1 (FINEMET) amorphous melt-spun ribbons did not exhibit devitrification or copper clustering. Differences in the magnetic properties were observed, with the Fe77.5Si13.5B9 and Fe76.5Si13.5B9Cu1 alloys exhibiting higher saturation magnetization (MS) and higher coercivity (HC) values while Fe74.5Si13.5B9Nb3, and Fe73.5Si13.5B9Nb3Cu1 alloys exhibited lower values of both these properties. These results clearly reveal the enhanced stability of the amorphous phase due to the addition of Nb in Fe–Si–B based melt-spun samples.

A computational study of diffusion in a glass-forming metallic liquid

Abstract: Liquid phase diffusion plays a critical role in phase transformations (e.g. glass transformation and devitrification) observed in marginal glass forming systems such as Al-Sm. Controlling transformation pathways in such cases requires a comprehensive description of diffusivity, including the associated composition and temperature dependencies. In the computational study reported here, we examine atomic diffusion in Al-Sm liquids using ab initio molecular dynamics (AIMD) and determine the diffusivities of Al and Sm for selected alloy compositions. Non-Arrhenius diffusion behavior is observed in the undercooled liquids with an enhanced local structural ordering. Through assessment of our AIMD result, we construct a general formulation for Al-Sm liquid, involving a diffusion mobility database that includes composition and temperature dependence. A Volmer-Fulcher-Tammann (VFT) equation is adopted for describing the non-Arrhenius behavior observed in the undercooled liquid. The composition dependence of diffusivity is found quite strong, even for the Al-rich region contrary to the sole previous report on this binary system. The model is used in combination with the available thermodynamic database to predict specific diffusivities and compares well with reported experimental data for 0.6 at.% and 5.6 at.% Sm in Al-Sm alloys.

Thermal, Structural and Crystallization Study of Niobium Potassium Phosphate Glasses

Abstract: New glass compositions were investigated in the binary system KPO3-Nb2O5. The glass forming domain was determined by melt-quenching of the starting nominal compositions and it has been experimentally observed that glass samples can be obtained between the molar compositions 95KPO3-5Nb2O5 and 50KPO3-50Nb2O5. Chemically stable compositions from 80KPO3-20Nb2O5 to 50KPO3-50Nb2O5 were characterized by DSC for determination of characteristic temperatures Tg, Tx, Tp and Tf. Glass transition temperatures strongly increase with Nb2O5 content whereas thermal stability against devitrification progressively decreases. Thermal data were used to suggest a structural model in which NbOx polyhedra are inserted inside the phosphate chains of PO4 units. For higher Nb2O5 contents, NbOx units progressively link together to form amorphous NbOx clusters, responsible for the yellow color and lower thermal stability against devitrification. For the composition 50KPO3-50Nb2O5, it has been found that the first crystallization peak is related with precipitation of hexagonal Nb2O5 in the glass matrix whereas the high temperature exothermic peak is due to both phase transition of hexagonal niobium oxide to monoclinic niobium oxide and precipitation of niobium potassium phosphate K2Nb6P4O26.

Method of cryogenic surface activation direct bonding for preparation of quartz glass capillary tube

Abstract: The present invention discloses a method of cryogenic surface activation direct bonding for preparation of a quartz glass capillary tube. According to the method, a wet chemical method is used to activate a quartz glass surface, and the manner of direct bonding of a stack of multiple layers of glass is applied, so as to prepare the quartz glass capillary tube at a lower temperature with a proper pressure. A steel needle of a specific size is added to a model and used to define a size and location of the capillary tube. The minimum diameter of the capillary tube prepared can reach as small as 200 micrometers ,and the bonding strength can reach 5 MPa. According to the method, the operation of cryogenic surface activation bonding is simple, the requirement on the glass sheet surface roughness is low, and no clean room or expensive ultra-high vacuum plasma treatment device is required. The method overcomes the problems of the pipe collapse, the device superficial devitrification and the inner wall roughness that may be caused by the conventionally prepared capillary tubes. The capillary tube produced has the smooth inner wall, increases the viewable region of the sample in the capillary tube, and dramatically improves chip performance.

The atomic-scale nucleation mechanism of NiTi metallic glasses upon isothermal annealing studied via molecular dynamics simulations.

Abstract: Nucleation is one of the most essential transformation paths in phase transition and exerts a significant influence on the crystallization process. Molecular dynamics simulations were performed to investigate the atomic-scale nucleation mechanisms of NiTi metallic glasses upon devitrification at various temperatures (700 K, 750 K, 800 K, and 850 K). Our simulations reveal that at 700 K and 750 K, nucleation is polynuclear with high nucleation density, while at 800 K it is mononuclear. The underlying nucleation mechanisms have been clarified, manifesting that nucleation can be induced either by the initial ordered clusters (IOCs) or by the other precursors of nuclei evolved directly from the supercooled liquid. IOCs and other precursors stem from the thermal fluctuations of bond orientational order in supercooled liquids during the quenching process and during the annealing process, respectively. The simulation results not only elucidate the underlying nucleation mechanisms varied with temperature, but also unveil the origin of nucleation. These discoveries offer new insights into the devitrification mechanism of metallic glasses.

Relations between thermal history and secondary structures of ignimbrites exclusive of rheomorphism

Abstract: Newly calculated model density profiles of ignimbrites also provide model thermal histories, which serve as a framework to help analyze the development of cooling joints, devitrification textures, and lithophysal cavities. Only those parts of sections of Rattlesnake Tuff in central Oregon that resided >600 °C for at least two years show devitrification. Low tensile strength means that joints form by thermoelastic contraction after cooling by as little as 25 °C. This means that columnar joints formed in as little time as a few weeks after deposition of the Aravaipa Tuff in SE Arizona. Compaction is rapid as well, so both columnar jointing and compaction are complete before the onset of devitrification in deposits <40 m thick. A section of Rattlesnake Tuff shows stratabound occurrences of devitrified spots and cavities; devitrification appears to have begun at scattered spots. Most spots are bounded by crescentic cavities in formerly ductile shards. The equation for conductive cooling of a spherical heat source shows that for rock volumes larger than ∼15 cm diameter, the rate of cooling is insufficient to prevent heating by latent heat by as much as 12 °C. Inflation therefore appears to have been caused by vapor released by devitrification and its slight adiabatic expansion. Eventual wholesale devitrification of matrix resulted in more-devitrified spots scattered in less devitrified matrix. Lithophysal cavities in the Rattlesnake Tuff and in the Peach Springs Tuff in NW Arizona are more abundant in lower density horizons, showing that cavity growth is favored in permeable zones between impermeable horizons. The Peach Springs Tuff and other deposits described in the literature have horizontal joints that formed during cooling and whose origin has yet to be deterministically modeled. The longest joints are most closely spaced in the zone of cavities and formed after columnar joints. It is inferred that after formation, each vertical column responds independently to evolving stresses; at this time, asperities together with gas pressures accompanying cavity formation result in horizontal joints. Columnar joints do not completely relieve growing gas pressures during devitrification, likely because of sealing by wholesale inflation of the rock mass and by mineral deposition. Some devitrified horizons of Rattlesnake Tuff and Peach Springs Tuff are densely fractured, resulting in a rubbly surface. These small fractures show zigzag traces, bifurcations, abrupt terminations, and pinch-and-swell walls, similar to ductile fractures described by [Eichhubl (2004)][1]. Their origin is interpreted to be the result of tensile stress due to porosity increase during later stages of devitrification. Closely adjacent sections of Rattlesnake Tuff at one site differ by 18% in thickness, reflecting buried paleotopography. Each section is devitrified. The thicker profile has a zone of lithophysal cavities near its base; the thinner profile has few cavities. The greater thickness translates to only 0.18 MPa additional lithostatic pressure at the base of the thicker profile, which serves to emphasize the subtle differences in initial conditions that can lead to formation of cavities. [1]: #ref-17

Thermal analysis of quaternary Ge – Se – Sb – Te chalcogenide alloys

Abstract: Tellurium-based glasses are suitable for storage devices due to their rapid amorphous-to-crystalline transformation. Alloys of Ge 19−y Se 63.8 Sb 17.2 Te y (y = 0, 2, 4, 6, 8, 10 at.%) have been synthesized using melt quench technique. Glass transition and crystallization kinetics of alloys have been investigated using differential thermal analysis at different heating rates (5, 10, 15, and 20 K min−1). The thermal stability of synthesized alloys has been investigated. Resistance to devitrification has been analyzed on the basis of activation energy for crystallization.

Metastable state of the Li 2 O-11.5GeO 2 glass-ceramics with a high electrical conductivity

Abstract: A glass of the Li2O-11.5GeO2 composition has been crystallized by heating and isothermal treatment near the devitrification temperature. The thermal properties and electrical conductivity σ of the glass in an alternating-current electric field have been investigated in the process of crystallization during the heating. The dependences σ(T) have been measured for isothermally crystallized Li2O-11.5GeO2 samples. Glass-ceramic samples in an intermediate metastable state with a high electrical conductivity have been synthesized by heat treatment of the initial glass. At T ∼ 500 K, the electrical conductivity of the intermediate state is one order of magnitude higher than that of the initial glass and three orders of magnitude higher than in the case of glass-ceramics consisting of Li2Ge7O15 crystallites and the GeO2 amorphous phase. It has been assumed that an increase in the electrical conductivity σ of the samples in the intermediate state is caused by the electrical conductivity of subsurface layers and is determined by the presence of a large number of nanometer-scale ordered regions in the structure.

Mass Balance and Atom Probe Tomography Characterization of Soft Magnetic (Fe 65 Co 65 ) 79.5 B 13 Si 2 Nb 4 Cu 1.5 Nanocomposites

Abstract: Electric and magnetic properties, including saturation induction, resistivity, Curie temperature, and others, that make soft magnetic materials attractive for applications such as power converters and electric machines depend on local alloy composition. In this paper, we address this dependence quantifiably. First, we correlate the crystallization state to local composition with a novel mass balance. Second, we perform atom probe tomography on (Fe65Co35)79.5B13Si2Nb4Cu1.5 magnetic nanocomposites to explore local compositional evolution with devitrification and test predictions. Precise 3-D atom maps of constituent elements are constructed from as-cast, intermediate, and late stage crystallized samples. Local compositions and final crystal fraction predicted from mass balances are tested. Analysis of chemical partitioning during growth quantifies the depletion of glass formers (GFs) in nanocrystals, and enrichment of GFs and depletion of Fe and Co in the amorphous phase. Finally, we demonstrate the direct measurement of local composition on a nanometer scale and present predictive models necessary to deduce intrinsic constituent phase properties and investigate the proposed shell interfacial phases.

The Effect of High-Pressure Devitrification and Densification on Ballistic-Penetration Resistance of Fused Silica

Abstract: Recent experimental and molecular-level computational analyses have indicated that fused silica, when subjected to pressures of several tens of GPa, can experience irreversible devitrification and densification. Such changes in the fused-silica molecular-level structure are associated with absorption and/or dissipation of the strain energy acquired by fused silica during high-pressure compression. This finding may have important practical consequences in applications for fused silica such as windshields and windows of military vehicles, portholes in ships, ground vehicles, spacecraft, etc. In the present work, our prior molecular-level computational results pertaining to the response of fused silica to high pressures (and shear stresses) are used to enrich a continuum-type constitutive model (that is, the so-called Johnson-Holmquist-2, JH2, model) for this material. Since the aforementioned devitrification and permanent densification processes modify the response of fused silica to the pressure as well as to the deviatoric part of the stress, changes had to be made in both the JH2 equation of state and the strength model. To assess the potential improvements in respect to the ballistic-penetration resistance of this material brought about by the fused-silica devitrification and permanent densification processes, a series of transient non-linear dynamics finite-element analyses of the transverse impact of a fused-silica test plate with a solid right-circular cylindrical steel projectile were conducted. The results obtained revealed that, provided the projectile incident velocity and, hence, the attendant pressure, is sufficiently high, fused silica can undergo impact-induced devitrification, which improves its ballistic-penetration resistance.

Densification and devitrification of fused silica induced by ballistic impact: a computational investigation

Abstract: A molecular-level computational investigation is carried out to determine the dynamic response and material topology changes of fused silica subjected to ballistic impact by a hard projectile. The analysis was focused on the investigation of specific aspects of the dynamic response and of the topological changes such as the deformation of highly sheared and densified regions, and the conversion of amorphous fused silica to SiO2 crystalline polymorphs (in particular, α-quartz and stishovite). The topological changes in question were determined by carrying out a postprocessing atom-coordination procedure. This procedure suggested the formation of stishovite (and perhaps α-quartz) within fused silica during ballistic impact. To rationalize the findings obtained, the all-atom molecular-level computational analysis is complemented by a series of quantum-mechanics density functional theory (DFT) computations. The latter computations enable determination of the relative potential energies of the fused silica, α-quartz and stishovite, under ambient pressure (i.e., under their natural densities) as well as under imposed (as high as 50GPa) pressures (i.e., under higher densities) and shear strains. In addition, the transition states associated with various fused-silica devitrification processes were identified. The results obtained are found to be in good agreement with their respective experimental counterparts.

Role of chain dynamics and topological confinements in cold crystallization of PLA‐clay nanocomposites

Abstract: The effects of the addition of organically modified nanoparticles on molecular dynamics, and subsequently, crystallization parameters were investigated using temperature modulated differential scanning calorimetry, dynamic mechanical analysis, and rheological measurements. Cold crystallization was observed to occur, at higher temperatures compared to the pure sample, due to the formation of topological constraints and the increase of the rigid fraction of amorphous chains, trapped in the polymer-particle interphase. It was also found that in the nanocomposites, the competition between the heterogeneous nucleating role of the nanoparticles and the restricted morphology effect on crystallization kinetics depends on devitrification of the rigid amorphous chains, at the isothermal crystallization temperature, and during nonisothermal crystallization. It was illustrated that the fraction of rigid amorphous chains, extended at the crystal-amorphous interphase, was enhanced by the increase of the overall crystallization rate. Moreover, the internal structure of the crystalline domains was revealed through small angle X-ray scattering. A correlation function was applied to SAXS data to estimate the long period and the thickness of alternatively stacked lamellae. It was demonstrated that the long period depends on the overall crystallization rate, which was found to be influenced by nanoparticle content. In contrast, the lamellae thickness did not show a noticeable variation with the addition of the nanoparticles. POLYM. ENG. SCI., 55:1310–1320, 2015. © 2015 Society of Plastics Engineers