INFLUENCE OF DILUENTS AND PLASTICIZERS ON THE PROPERTIES OF EPOXY-POLYSULFIDE COMPOSITES

It was found that to increase the adhesive and physicomechanical properties of compositions based on epoxy resin and polysulfide rubber (thiokol), cured without heat treatment, it is necessary to carry out a preliminary thioetherification reaction (PRTE) due to the interaction of rubber mercaptan groups and oxirane cycles of epoxy resin at elevated temperatures and then use the product of this reaction to cure at room temperature. Composite materials based on the products of the thioetherification reaction significantly surpass analogs based on mechanical mixtures of epoxy resin and thiokol in terms of cohesive and adhesive strength, deformation capacity, fracture work, and specific impact strength. It is shown that the introduction of both diluents and plasticizers into the products of the preliminary thioetherification reaction of epoxy resins and polysulfide rubbers leads to an increase in the parameters of tensile strength and deformation capacity. The greatest strengthening effect is achieved with the use of oligoesteracrylate MGF-9 and glycidyl ether of diethylene glycol DEG-1, the smallest - with the introduction of the plasticizer EDOS. It was found that the introduction of plasticizers promotes some increase in the adhesive strength, but much less in comparison with the cohesive strength. In this case, the adhesion and cohesive characteristics change antibatically. It has been shown by dynamic mechanical spectrometry that the presence of diluents and plasticizers in epoxy-polysulfide composites leads to a decrease in the temperatures of the maximum values of the tangent of the angle of mechanical losses, loss modulus, the initial and final sections of the transition of the material from the glassy to the highly elastic state, as well as the density of the chemical network in the epoxy matrix.

Properties of epoxy-thiokol materials based on the products of the preliminary reaction of thioetherification

In order to improve the adhesive and physical-mechanical properties of epoxy-thiocol compositions cured without heat treatment, we propose to carry out the reaction of interaction between thiokol mercaptan groups and oxirane cycles of epoxy resin at an elevated temperature before introducing a curing agent, and then use the product of this thioetherification reaction for curing at room temperature. The temperature range of the thioetherification reaction (90–1800С) was determined by the method of differential scanning calorimetry. The optimal temperature (1600С) and duration of the preliminary thioetherification reaction (2 hours) were determined, which ensure the maximum level of adhesive strength and physical-mechanical properties. It was shown that composite materials based on the products of the thioetherification reaction significantly outperform analogs based on mechanical mixtures of epoxy resin and thiokol in terms of cohesive and adhesive strength, deformation capacity, fracture work and specific impact strength. The impact resistance and shear strength of adhesive joints are especially significantly increased during the curing of the compositions without external heat supply.

RAPID ASSESSMENT OF POZZOLANIC ACTIVITY IN DETERMINING THE EFFECTIVENESS OF EXPANSIVE SULFO-ALUMINATE TYPE ADDITIVES ABSTRACT

Применение расширяющихся добавок на основе сульфоалюминатных композиций для модификации цементных систем позволяет не только компенсировать усадку, но в ряде случаев получить расширение и самонапряжение. На сегодняшний день рынок изобилует расширяющимися добавками на основе сульфоалюминатных композиций, представляющими собой как искусственно синтезированные материалы, так и механические смеси на основе метакаолина, глиноземистого цемента и гипса (цемент типа «М»). Выбор того либо иного вида добавки, а также ее дозировка назначаются в зависимости от проектных требований к бетону: компенсация усадки, достижение требуемых величин линейного расширения и самонапряжения и т. п. Каждый индивидуальный случай применения такого рода добавок в бетоне требует дополнительных исследований в бетоне по действующим ТНПа, которые занимают от 14 до 28 сут. В ряде случаев такой период испытаний является слишком длительным, и требуются ускоренные методы определения эффективности. В данной статье представлены исследования возможности применения в качестве одного из критериев эффективности расширяющейся добавки пуццолановой активности. Обоснована возможность определения пуццолановой активности по ускоренной методике Чапеля, что позволит в короткий период времени (1-2 сут) определиться с выбором той либо иной расширяющейся добавки. В качестве исследуемых добавок рассмотрены расширяющиеся комплексы на основе механических смесей глиноземистого цемента и гипса, метакаолина и гипса, также с добавлением извести. Предложен диапазон необходимых для получения цементов с компенсированной усадкой или самонапряжением 1 МПа значений пуццолановой активности. The use of expansive additives based on sulpho-alumina compositions to modify cement systems not only compensates for shrinkage, but in some cases allows for expansion and self-stressing. Today the market is replete with expansive additives based on sulfoaluminate compositions, which are both artificially synthesized materials and mechanical mixtures based on metakaolin, high alumina cement and gypsum (type “M” cement). The choice of a particular type of additive, as well as its dosage, is determined depending on the design requirements for concrete: shrinkage compensation, achieving the required values of linear expansion and self-stress, etc. Each individual case of this type of concrete admixture requires additional research in concrete under the existing norms, which take 14 to 28 days. In some cases, such a test period is too long and requires accelerated methods to determine efficiency. This article presents research into the possibility of using the pozzolana activity of expansive additive as one of the performance criteria. It has been substantiated that pozzolanic activity can be determined using the accelerated Chapelle test, which will allow a short period of time (1-2 days) to determine the choice of a particular expansive additive. Expansive complexes based on mechanical mixtures of alumina cement and gypsum, metakaolin and gypsum, also with the addition of lime, have been considered as additions under study. The range of pozzolanic activity values required to produce cements with compensated shrinkage or self-stress of 1 MPa is proposed.

The composition of the vapor phase upon evaporation of a mechanical mixture of cadmium and zinc selenotelluride powders

The effect temperature has on the composition of a vapor phase passed through a thermal field after the evaporation of a mechanical mixture of the powders of cadmium and zinc selenotelluride is studied. It is found that the composition of the vapor phase can be changed throughout the range of concentrations by varying the temperature. The results of the study are satisfactorily explained by the effect temperature has on the particle distribution function in correspondence to the weights of the molecules constituting the mixture. There were virtually no molecules of the evaporated substance in the vapor phase, which consisted of diatomic molecules of the elements of Group VX compounds and metal atoms. This means that with the evaporation of mechanical mixtures of CdTe and CdSe powders, the vapor phase in the evaporator contains only Cd, Se2, and Te2 molecules, while mixtures of ZnTe and ZnSe powders contain Zn, Se2 and Te2 molecules. Despite the similarity between the components’ heats of sublimation, their concentrations over the powdermixture did not correspond to the composition of the powder mixture, since compounds A2B6 sublimate incongruently. Coming from the evaporator, the vapor phase entered the thermal field and was condensed onto a substrate at room temperature at its outlet. As follows from the composition of the substrate films, the vapor phase at the outlet was enriched with the light component Se, compared to the powder mixture. By virtue of the law of the conservation of mass, the vapor phase was therefore enriched with the heavy component Te at the inlet to the thermal field. Our results show that the thermal field controls the composition of the vapor phase by changing the particle distribution function according to the weight of the molecules constituting the mixture. The temperature dependences of the composition of the vapor phase are presented for several mechanical mixtures of the powders of (CdSe)x (CdTe)1-x and (ZnSe)x (ZnTe)1-x, where x = 0.45-0.90.

Optimization of the coating process by cold gas dynamic spraying applied to production conditions of Ni–Ti and Ni–Al systems

This study developed practical recommendations for using the method of cold gas dynamic spraying to obtain functional coatings in a production environment using powders of nickel, titanium and aluminum of the grades: PNE-1 (Ni), PTOM-1 (Ti) and PA-VCh (Al). The temperature and speed parameters of the process were optimized using mechanical mixtures (Ni + Ti) and (Ni + Al) as an example. High adhesion of the coating and coefficient of powder use were ensured with maximum productivity at the DIMET-403 installation.

Effect of the catalytic system and operating conditions on BTX formation using tetralin as a model molecule

Light cycle oil (LCO) is an inexpensive feedstock for the production of high-added-commercial-value-mono-aromatic compounds such as benzene, toluene and xylenes (BTX). To extend the knowledge on the processing of LCO for BTX production, the hydrocracking reaction was studied using a commercial NiMo/Al2O3 catalyst, ZSM-5 zeolite and their mechanical mixtures (20/80, 30/70 and 50/50) for processing tetralin as model feedstock in a bench-scale-trickle-bed reactor at 450–500 °C, 3.9–5.9 MPa, 1.3 1/h and H2/feed volume ratio of 168–267 m3/m3. Accessible, well-dispersed and strong Brönsted acid sites eased the hydrocracking of tetralin to BTX and the metallic hydrogenation functions from nickel–molybdenum catalysts were also required to minimize deactivation. To achieve suitable tetralin conversions (86–95 wt%), high BTX selectivity in the liquid phase (44–70 wt%) and suitable catalytic activities for coke precursor hydrogenation (to reduce deactivation), NiMo/Al2O3//ZSM-5 mixtures (50–80 ZSM-5) were employed, which probed to be effective.

Hydrogen Desorption in Mg(BH4)2-Ca(BH4)2 System

Magnesium borohydride, Mg(BH4)2, and calcium borohydride, Ca(BH4)2, are promising materials for hydrogen storage. Mixtures of different borohydrides have been the subject of numerous researches; however, the whole Mg(BH4)2-Ca(BH4)2 system has not been investigated yet. In this study, the phase stability and the hydrogen desorption were experimentally investigated in the Mg(BH4)2-Ca(BH4)2 system, by means of XRD, ATR-IR, and HP-DSC. Mg(BH4)2 and Ca(BH4)2 are fully immiscible in the solid state. In the mechanical mixtures, thermal decomposition occurs at slightly lower temperatures than for pure compounds. However, they originate products that cannot be identified by XRD, apart from Mg and MgH2. In fact, amorphous phases or mixtures of different poorly crystalline or nanocrystalline phases are formed, leading to a limited reversibility of the system.

SYNTHESIS OF GLYCIDYL AND THIOGLYCIDYL ETHERS OF DIACETYLENE SERIES AND THEIR USE AS A MODIFIER OF PHENOL-FORMALDEHYDE OLIGOMERS

It has been shown that the chlorine-containing unconjugated enyne alcohols react with epichlorohydrin in the presence of boron trifluoride etherate with formation of chlorohydrines, which further without their isolation, under the action of potassium hydrochloride are dehydrochlorinated with formation of the corresponding glycidyl ethers. Under the action of an alcoholic solution of potassium hydroxide at temperature of 75-80 °С on synthesized chlorine-containing ethers the dehydrochlorination reaction on double С=С bond proceeds and glycidyl ethers of 1,4-diine series are formed. It has been revealed that the synthesized glycidyl ethers are the very reactive compounds. In patricular, it has been shown that the ethers of 1,4-diine series with the participation of oxirane ring undergo the reaction with thiurea medium of methanol at 30-35 °С, forming the corresponding tyrants. The data of IR- and NMR-spectra of the prepared compounds have been presented and their modifying properties in relation to phenol-formaldehyde oligomers in acidic and alkaline media have been revealed. The prepared modified oligomers are the products of liquid-viscous consistency, soluble in acetone, tetrahydrofuran, dimethyl formamide and dioxane. It has been proved by the carried out analyses that the prepared PhFOs, modified by glycidyl and thiglycidyl ethers of diacetylene series are not mechanical mixtures of phenol, formaldehyde and modifier. On the basis of obtained results the formation mechanism of modified resol and novolac PhFO has been also revealed. It has been established that the physical-chemical and physical-mechanical parameters of the prepared phenol-formaldehyde oligomers modified by modifiers proposed by us, in comparison with unmodified ones, are improved. From the proposed diglycidyl and thiodiglycidyl ethers for the modification of PhFO the best results on all parameters are achieved at modification with thioglycidyl ether of diacetylene series.