Chemical Curing Research Articles

Experimentally Investigation of Curing Shrinkage of Extra Low Dilated Epoxy by Fiber Bragg Gratings

The bonding adhesion with low shrinkage and coefficient of thermal expansion is really important for packaging of the photonic and optoelectronic elements. Lots of the thermoset glue is thus developed for this packaging. however, the curing shrinkage of the adhesion is relatively large. The silica filler is usually mixed into the epoxy for lowering the curing shrinkage and the CTE. In this study, the filler with negative CTE is derived to decrease the CTE and shrinkage of the composite epoxy. The fiber Bragg gratings is built in the composite of epoxy/filler. The adhesive composite is then put into the temperature cycle chamber for curing. At the meanwhile the FBGs during curing is on-line monitored by the Optical Oscillation Analyzer. Measuring the variation of the central wavelength of FBGs, the curing shrinkage of the composite epoxy with NCTE filler can be is derived. The results show that axial stress is increased drastically during the chemical curing stage. By application of this NCTE filler/epoxy adhesion, the property of the lower shrinkage is expected.

Traditional medicine: Where does it stand?

While earth is becoming a smaller village every day, the rapid population growth and ageing is impeding obvious shifting pattern of disease which in turn is inflecting great economic burden required for fast growing health expenditure particularly in the developing world whose suffering from this particular issue is turning into an inflated almost non-curable disease. The major world population today is suffering from poverty and week health status mainly in countries that find it extremely difficult to have proper plans and programs capable of solving such serious dull future. Conventional Medicine with all its astonishing advancements still cannot satisfy public health demands a fact that could be generalized to all societies today but it is of very much concern to mankind in the developing countries. The serious challenges imposed on such societies to maintain reasonable healthy conditions are placing the Traditional Medicine in a very special position where some times willingly or compulsory it is holding a noticeable share in the health care delivery systems, some times officially recognized and some times without any national control socially accepted. Scientists, Policy makers, Health care deliverers, Academies and International Organizations such as WHO are well aware of the great value of Traditional Medicine a matter that has been well reflected in many local and international meetings designed to reflect this fact and one can name few important ones held at the beginning of this century ; “WHO International Symposium on Traditional Medicine, September 11-13, 2000, Japan“ and “The International Consultative Meeting on Global Information on Traditional Medicine, WHO Kobe Center, September 19-21, 2001, Japan” and “The International Seminar on Integration of Traditional Medicine and Modern Medicine, October 12-15, 2002 in Cairo“ and “International Meeting on Global Atlas of Traditional Medicine, Kobe, June 17-19, Japan“. Despite very serious attention paid to Traditional Medicine the fact remains though it is still under estimated, not regulated and misconceived while majority of countries worldwide are not giving it the weight it carries or deserves and not defined in the category of national programs intended for health care delivery systems and social welfare strategies. In addition academic curricula is strongly lacking practical revision of the role of Traditional Medicine in their educational set up to produce manpower capable of utilizing this rather important growing need as a skill required to meet national health needs. Interestingly one can feel a global human desire to replace pure chemical curing agents with natural remedies and treatments a matter that worth emphasizing and demands special attention since we who care to provide satisfactory health care are responsible to respond to the clients wish and needs.

Modeling early-age hydration kinetics of Portland cement using flexible neural tree

The early-age hydration of Portland cement paste has an important impact on the formation of microstructure and development of strength. However, manual derivation of analytic kinetic equation for hydration process is very difficult because there are multi-phased, multi-sized and interrelated complex chemical and physical reactions during cement hydration. In this paper, a flexible neural tree structure is built as the right-hand side of kinetics instead of traditional analytic expression. Two evolutionary algorithms gene expression programming and particle swarm optimization are used to evolve tree structure and rules’ parameters, respectively. In order to reduce the computing time, GPUs are used for acceleration in parallel. Studies have shown that according to the established model, simulation curve of early-age hydration is in good accordance with the observed experimental data. Furthermore, this model still has a good generalization ability even changing chemical composition, particle size and curing conditions.

Reverse extraction of early-age hydration kinetic equation from observed data of Portland cement

The early-age hydration of Portland cement paste has an important impact on the formation of microstructure and development of strength. However, manual derivation of hydration kinetic equation is very difficult because there are multi-phased, multi-sized and interrelated complex chemical and physical reactions during cement hydration. In this paper, early-age hydration kinetic equation is reversely extracted automatically from the observed time series of hydration degree of Portland cement using evolutionary computation method that combines gene expression programming and particle swarm optimization algorithms. In order to reduce the computing time, GPUs are used for acceleration in parallel. Studies have shown that according to the extracted kinetic equation, simulation curve of early-age hydration is in good accordance with the observed experimental data. Furthermore, this equation still has a good generalization ability even changing chemical composition, particle size and curing conditions.

Quantification of simultaneous solvent evaporation and chemical curing in thermoset coatings

The mechanisms of simultaneous solvent evaporation and film formation in high-solids thermoset coatings are considered. The relevant phenomena, chemical reactions, solvent diffusion and evaporation, gelation, vitrification, network mobility restrictions, and crosslinking, are quantified and a mathematical model for a curing film is presented, which does not violate the local volume balance. For model verification, a previous investigation with a polyisocyanate and a polyol in methyl amyl ketone solvent, catalyzed by an organotin compound, was selected. In contrast to earlier modelling studies, simulations can match and explain detailed experimental data. For exemplification, simulations are used to analyse the influence of the various rate phenomena on the behavior of the solvent-based polyisocyanate/polyol film.

Influence of filling technique and curing mode on the bond strengths of composite cores to pulpal floor dentin

This study evaluated the influence of filling technique and curing mode on the microtensile bond strengths (MTBS) of composite cores to pulpal floor dentin. Access cavities of human molars with pulpal floor dentin were restored with a two-step self-etch adhesive system, Clearfil Liner Bond 2V and a composite core, Clearfil DC Core Automix, using different filling techniques and curing strategies. A flowable resin composite, Clearfil Flow FX was placed on the cured adhesive resin prior to restoration with a composite core. Packing the composite in the access cavity was performed in bulk with or without light curing or using an incremental technique with light curing. Microtensile bond strengths to pulpal floor dentin were measured after 24 hours storage in water. Light curing and incremental technique had positive effects on the MTBSs. Lining with a flowable resin composite did not significantly improve the MTBSs, however, influenced the failure mode after debonding. Non-lining and bulk filling with chemical curing strategy provided the lowest MTBS.

Degree of vinyl conversion, polymerization shrinkage and stress development in experimental endodontic composite.

This study explores degree of vinyl conversion (DVC), polymerization shrinkage (PS) and shrinkage stress (PSS) of the experimental amorphous calcium phosphate (ACP) composites intended for use as an endodontic sealer. Light-cure (LC), chemical cure (CC) or dual-cure (DC; combined light and chemical cure) resins comprised urethane dimethacrylate (UDMA), 2-hydroxyethyl methacrylate (HEMA), methacryloyloxyethyl phthalate (MEP) and a high molecular mass oligomeric co-monomer, poly(ethyleneglycol)-extended UDMA (PEG-U) (designated UPHM resin). To fabricate composites, a mass fraction of 60 % UPHM resin was blended with a mass fraction of 40 % as-made (am-ACP) or ground ACP (g-ACP). DVC values of copolymer (unfilled UPHM resin) and composite specimens were determined by infrared spectroscopy. Glass-filled composites were used as controls. PS and PSS of composites were determined by dilatometry and tensometry, respectively. LC copolymers attained extraordinary high DVC values at 24 h post-cure (95.7 %), compared to CC (52 %) and DC (79.3 %) copolymer specimens. While the DVC values of LC and DC am-ACP composites were reduced between 5 and 10 %, DVC values of DC g-ACP composites increased almost 8 % compared to the corresponding copolymers. High DVC attained in LC composites was, expectedly, accompanied with high PS values (on average 7 vol%). However, PSS developed in LC and especially DC composites did not exceed PSS values seen in other UDMA-based composites. Based on this initial evaluation, it is concluded that, DC, g-ACP filled UPHM composite shows promise as an endodontic sealer. However, further physicochemical evaluations, including water sorption, mechanical stability and ion release as well as a leachability studies need to be performed before this experimental material is tested for cellular responses and, eventually recommended for clinical utility.

The Myth of the Chemical Cure: A Critique of Psychiatric Drug Treatment

The Myth of the Chemical Cure: A Critique of Psychiatric Drug Treatment . Joanna Moncrieff. New York: Palgrave Macmillan, 2008, 278 pp., $95.00. In the gloomiest of days during the American Revolution when George Washington's soldiers were enduring a cold, poorly clothed, and hungry winter at Valley Forge in December 1776, Tom Paine wrote, "These are the times that try men's souls. The summer soldier and the sunshine patriot will, in this crisis, shrink from the service of their country." There is something of a gloom hanging over the revolution against involuntary, biological psychiatry. Like the British Empire at the time of American's War of Independence, organized psychiatry and the drug companies have all the money, all the power, and most of the big victories. What does the opposition to modern psychiatry have on its side? What armaments are in the hands of those few who stand up for independence from oppressive and irrational biological psychiatry? We have the scientific truth and right principles, at this point spoken by a few undaunted, courageous truth speakers. Joanna Moncrieff is one of these few truth speakers. I should begin with a disclosure of conflict of interest. Joanna Moncrieff and I get together on occasion at professional meetings, we've shared a couple of speech platforms in London, and I like her and respect her very much. We correspond occasionally. She is a board member of the International Center for the Study of Psychiatry and Psychology, the organization I founded decades ago. If she didn't live on that island (England) so far away, I'm sure we'd know each other better. So I was prepared to like her book and maybe, unconsciously, to be generous toward her. Why generous? Because long ago I learned to mute my disappointment with my colleagues in psychiatry-even the ones I like. No disappointment here! Dr. Moncrieff's book impressed me with its scientific precision, its incisiveness, its honesty, and its courage. She masterfully weaves together science and philosophy. Although written from a scientific perspective, the prose is incisive. She writes with a rare determination to make herself clear and accomplishes her aim with easily readable prose. She does not waffle about her conclusions as one might expect by a psychiatrist with academic credentials and appointments. The Myth of the Chemical Cure: A Critique of Psychiatric Drug Treatments delivers what is says it will. Dr. Moncrieff sets her observations within two alternative models of explanations. One is biological model, which she calls the disease-centered model. Its first two premises are "Drugs help an abnormal brain state" and "Therapeutic effects of the drugs derived from their effects on presumed disease pathology." The paradigm, of course, is insulin for diabetes. Dr. Moncrieff proposes and ultimately defends a second paradigm, the drug-centered model. This drug-centered model begins by understanding how drugs really work. Its first two premises are "Drugs create an abnormal brain state" and "Therapeutic effects derived from the impact of the drug-induced state on behavioral and emotional problems." The model is alcohol for anxiety. She debunks the notion that psychiatric drugs are specific for diseases and cites scientific literature calling into question claims for effectiveness. …

Effect of CNT surface functionalisation on the mechanical properties of multi-walled carbon nanotube/epoxy-composites

The use of carbon nanotubes (CNTs) as filler material for the mechanical reinforcement of plastics requires an effective surface functionalisation in order to allow the integration of CNTs into the molecular structure of the matrix. Some of these additives have an effect on the chemical structure, thus changing the mechanical properties of the investigated epoxy. This paper examines the extent of matrix reinforcement achieved through the addition of CNTs, functionalised CNTs and a variety of additives. It is shown that the mechanical improvements of the matrix are due mainly to the modification of the chemical curing reaction and only to a small degree to the CNTs.

Characterization of Chemical Cure Shrinkage of Epoxy Molding Compound With Application to Warpage Analysis

After encapsulation, thermomechanical deformation builds up within the electronic packages due to the temperature coefficient of expansion mismatch between the respective materials within the package as it cools to room temperature. At the same time, the chemical cure shrinkage exerts important influence on the total deformation. Due to the complexity and time consuming of the calculation, it is almost impossible for an industry to carry out the numerical simulation using viscoelastic property, which is the most close to the real material property of polymer material. However, finite element analysis (FEA) using temperature-dependent elastic property, temperature-dependent thermal expansion coefficient, and accurate chemical cure shrinkage can help to improve the accuracy on the stress and warpage prediction. This study has developed an evaluation method for the chemical cure shrinkage based on the measurement of the warpage of bimaterial model. The results show that FEA simulations without chemical cure shrinkage fail to accurately predict the package warpage. On the other hand, FEA simulations with chemical cure shrinkage are outlined, which show fair agreement with experimental measurements of package warpage over a range of temperatures. Furthermore, this study has evaluated the effect of silica filler percentage on the chemical cure shrinkage and confirmed that the chemical cure shrinkage decreases with the increase in silica filler percentage.

Evaluation of the effectiveness of methods of physical modification in production of reinforced thermosetting plastics

It is proposed that the efficacy of different methods of physical modification be evaluated with the physicochemical activity of the physical effects that unavoidably affect the rate of chemical curing. Of the three methods of physical modification examined, treatment of prepregs with ultraviolet radiation and exposure to a constant electric field can be considered the most reliable and effective.

The impact of cement mixing and storage errors on the risk of failure of glass–ceramic crowns

This study evaluated the impact of different mixing ratios and wrongly stored blends of dual-curing composite cements on Empress2 glass-ceramic crowns by means of a flexural strength test and a fracture resistance test. Thermally damaged blends and fresh blends were mixed using different mixing ratios of dual-curing Panavia F and Variolink II composite cement (2:1; 1:1; 1:1.5; 1:1.75; base/catalyst). Sixteen groups of rectangular beams of both cements (two blends, four ratios, chemical-curing, light-curing) were constructed. Their flexural strength was determined in a three-point bending test. Furthermore, 64 Empress2 all-ceramic crowns were luted onto human molars, again using fresh and thermally damaged blends as well as different mixing ratios of the luting agents. After aging, fracture resistance was investigated. The flexural strength of dual-curing composite cements was influenced to a statistically significant extent by mixing ratios and storage conditions. In particular, the chemical curing mode of these cements was affected by the thermal damage of the blends. However, this study could not demonstrate a significant impact on the fracture resistance of Empress2 glass-ceramic crowns when different mixing ratios or wrongly stored cements were used. Dual-curing composite luting agents seem to tolerate a wide range of mixing errors, but their chemical curing mode may be affected by storage errors.

The myth of the chemical cure: a critique of psychiatric drug treatment

The Disease Centred Model of Drug Action in Psychiatry An Alternative Drug Centred Model of Drug Action Physical Treatments and the Disease Centred Model The Arrival of the New Drugs and the Influence of Interest Groups The Birth of the Idea of an 'Antipsychotic' Are Neuroleptics Effective and Specific? A Review of the Evidence What do Neuroleptics Really Do? A Drug Centred Approach The Construction of the 'Antidepressant' Is There Such a Thing as an Antidepressant? A Review of the Evidence What do Antidepressants Really Do? The Idea of Special Drugs for Manic Depression Evidence on the Action of Lithium and Mood Stabilisers Democratic Drug Treatment: Implications of the Drug Centred Model The Myth of the Chemical Cure

Hugh Trevor-Roper, Europe's physician: the various life of Sir Theodore Turquet de Mayerne, New Haven and London, Yale University Press, 2006, pp. xii, 438, illus., £25.00, US$35.00 (hardback 0-300-11263-7).

Hugh Trevor-Roper, Europe's physician: the various life of Sir Theodore Turquet de Mayerne, New Haven and London, Yale University Press, 2006, pp. xii, 438, illus., £25.00, US$35.00 (hardback 0-300-11263-7). - Volume 52 Issue 3

Personal Accounts: More Magic Bullets?

Personal Accounts: More Magic Bullets?

Personal Accounts: More Magic Bullets?

Personal Accounts: More Magic Bullets?

Preparation and Properties of SiC Fibers Containing Yttrium and Aluminum

SiC fibers containing Y and Al were prepared by sintering the amorphous KD-Y fibers at different temperatures from 1200 to 1800 °C. The tensile strength of fibers increases when the sintering temperature increases from 1200 to 1400 °C due to the dispersion strengthening of β-SiC microcrystal and decreases to the lowest point when being sintered at 1600 °C, then rose again with the further increase of temperature to 1800 °C. The tensile strength reached to 2.15 GPa. The oxygen content of KD-Y fibers determined the properties of the sintered SiC fibers and sintering process. Through chemical vapor curing (CVC), the oxygen content was controlled below 7.0 wt% and the tensile strength of KD-Y fibers reached to 3.08 GPa. Further-more, the sintering process of KD-Y fibers was discussed and the grain size of β-SiC grew up with the heat treatment temperature.

Light- and time-dependent polymerization of dual-cured resin luting agent beneath ceramic

Objective. In this study we investigated the degree of conversion (DC) of a dual-cured resin luting agent beneath a ceramic of different thickness. Material and Methods. The luting material (RelyX) was photo-activated for 40s through ceramic disks (Empress Esthetic, 0.7, 1.4, or 2mm thick). Dual (DUC) and chemically cured (CC) control groups were obtained. A delayed exposure (DE) procedure was tested in which the material was light-activated after 5 min without using ceramic. DC (%) was measured using infrared spectroscopy at 40 s, 1, 2, 4, 6, 8, and 10min. Light irradiance and spectrum transmitted through ceramic were measured using a power meter and a spectrometer. Results. A decrease in irradiance was detected with increasing ceramic thickness, but no alteration in the emission profile was observed. At 10min, all groups showed DC higher than at 40s. No significant differences were detected for DUC compared with the groups indirectly activated through the ceramic disks. Generally, CC showed the lowest DC values. No significant effect in DC was detected for DE after 10min. A significant increase in DC was generally detected only up to 4min. Conclusions. The luting agent was dependent on light exposure and time to obtain improved DC. Neither the indirect activation nor the DE procedure significantly influenced the final DC.

Mechanical properties of provisional crown and bridge materials: Chemical-curing versus dual-curing systems

Objectives This study aimed to investigate the flexural strength (FS) and flexural modulus (FM) of provisional crown and bridge materials at different storage times after mixing using materials with different curing mechanisms (dual-curing vs. self-curing). Methods FS and FM of four proprietary materials (Trim, Luxatemp AM Plus, Luxatemp AM Plus Solar and Cool Temp Natural) were tested in a 3-point bending test according to EN ISO 4049:2000 at various times after mixing (37 °C dry/water) including thermocycling (5000×, 5–55 °C). Mean values of all measurements were calculated and subjected to the Games–Howell test ( p = 0.05) as well as a regression analysis ( p = 0.05). A two-way ANOVA ( p = 0.05) was used to identify the influence of the curing mechanism and chemical nature of the materials used. Results FS ranged between 11.1 and 24.0 MPa and FM between 82.5 and 548.2 MPa for all tested materials except for the dual-curing material (FS: 82.4 MPa; FM: 2060 MPa) 10 min after mixing. The r 2-values, describing the goodness-of-fit of the regression curve for the relation between the mechanical properties and storage time, ranged from 0.701 to 0.979 for the composite based materials and 0.671 to 0.685 for the methacrylate resin. The chemical nature and curing mechanism significantly influenced ( p < 0.001) the mechanical properties, however, the influence of the curing mechanism disappeared at progressive points in time after mixing comparing Luxatemp AM Plus versus Luxatemp AM Plus Solar. Conclusions FS and FM significantly depend on the time after mixing. Composite resin based materials are preferred versus methacrylate resins due to more favourable mechanical properties. If a high mechanical strength is indispensable directly after fabrication, a dual-curing provisional material is recommended.

Influence of ceramic thickness on mechanical properties and polymer structure of dual-cured resin luting agents

Objective To investigate the influence of ceramic thickness on the mechanical properties and polymer structure (degree conversion and cross-linking density) of three dual-cured resin luting agents. Methods Three dual-cured resin luting agents [Linkmax HV (GC), Nexus 2 (Kerr), and Variolink IIHV (Ivoclar-Vivadent)] were polymerized with or without 800 mW/cm 2 irradiation through 0–3-mm-thick GN-I (GC) machinable ceramic. Bar-shape specimens were subjected to three-point bending to determine flexural strength (FS) and elastic modulus (EM) after dry storage at 37 °C for 24 h. Knoop hardness was measured on the irradiated surface of disk-shaped specimens before (KHN1) and after (KHN2) storage of 100% ethanol solution at 37 °C for 24 h. KHN1 and KHN2 were estimated as indirect indicators of degree of conversion (DC) and cross-linking density, respectively. Data were analyzed by one-way ANOVA and Student–Newman–Keuls test for each luting agent, and four mechanical properties were subjected to regression analysis. Results For three resin luting agents with dual-cured mode, FS, EM, KHN1, and KHN2 decreased with the increase of ceramic thickness. FS except for Nexus 2 and EM for three resin luting agents had a positive linear relationship with both KHN1 and KHN2. Significance The variables tested behaved differently. When the ceramic thickness increased, the chemical cured components of dual-cured resin luting agents did not produce significant compensation for all variables. Mechanical properties and polymer structure of dual-cured resin luting agents was dependent on the intensity of light irradiation.