- TITLE:
DEVELOPMENT OF HYDROPHILIZED UNSATURATED POLYESTER RESINS BASED ON DIFFERENT TYPES OF MODIFIERS
- AUTHOR(S):
R. Cherkezova, T. Hristova, K. Zafirova
- ABSTRACT:
This work presents the modification of unsaturated polyester resin (UPER) with different types of
hydrophilizing components – sodium hydroxide, sulfur and sulfate-resistant cement. A different type
of hydrophilized unsaturated polyester resin (HUPER) was obtained based on this processing. The
varieties of HUPER so obtained were compared on the basis of their hardening kinetics. When
sodium hydroxide is used as a hydrophilizing agent minimum amounts of sodium hydroxide make it
possible to choose a minimum gelation time. Unlike the sodium hydroxide, the hydrophilizing agent
sulfur demonstrates that the increase in its amount results in lower gelation temperatures and
increases the gelation time. A special feature of the third hydrophilizing agent sulfate-resistant
cement was identified, whose amount does not affect the gelation time, i.e. it is maintained within
certain limits (27-29 min). A comparison of strength values was made. With the hydrophilizing agent
sodium hydroxide the test pieces retain their strength values in a broader range (2.99-4% tensile
elongation, 14.98-18.62 MPa tensile strength, 1056.81-581 MPa Young’s modulus). Where the
hydrophilizing agent is sulfur these values are the lowest, and the sulfate-resistant cement increases
to the greatest extent the tensile strength values (24.19 MPa) and percent tensile elongation values
(8.23%), and to the lesser extent – the Young’s modulus values (389.25 MPa).
- PAGES:
11-
- TITLE:
DIAMOND BURNISHING PROCESS EFFICIENCY TO INCREASE THE WEAR RESISTANCE OF SLIDING BEARING BUSHINGS MADE OF CuAl8Fe3 BRONZE
- AUTHOR(S):
G.V.Duncheva, A.P.Anchev, D.K.Drumeva
- ABSTRACT:
In this article, the object of the experimental study is wear resistance of sliding bearing bushings
made of CuAl8Fe3 bronze after diamond burnishing. Tribological studies were performed under
boundary lubricant conditions and dry friction conditions. In order to evaluate the efficiency of the
diamond burnishing process, a comparison of the wear characteristics of three groups of specimens
was made: treated only by cutting, subjected to diamond burnishing with one pass; subjected to
diamond burnishing with six passes. It has been proved that under boundary lubricant conditions,
the specimen subjected to diamond burnishing with six passes has 2.27 times higher wear resistance
compared to the wear resistance of the specimen treated by cutting, and 1.42 times higher wear
resistance than that of the specimen subjected to diamond burnishing with one pass. Under dry
friction conditions, the specimen subjected to diamond burnishing with one pass has 2.45 times
higher wear resistance than the wear resistance of the specimen treated by cutting, and lower wear
resistance than that of the specimen subjected to diamond burnishing with six passes. Applying of
diamond burnishing with six passes leads to 2.3 times higher wear resistance under dry friction
conditions compared to the conventional case of holes machining.
- PAGES:
1-
- TITLE:
CRYSTALLOGRAPHY OF COOPER OXIDE COATINGS DEPOSITED ON Si SUBSTRATE BY REACTIVE MAGNETRON SPUTTERING
- AUTHOR(S):
M. Ormanova, G. Kotlarski, D. Dechev, S. Valkov, N. Ivanov, P. Petrov
- ABSTRACT:
Copper oxide (CuO) is used in the photovoltaic (PV) industry and modern biomedicine. These
coatings are applied to increase the wear and corrosion resistance, and to improve the
biocompatibility of the materials.
In this work, copper oxide coatings were deposited on silicon substrates by reactive magnetron
sputtering. During the process, the substrate temperature was in the range from 100 °C to 400 °C
and the deposition time was 60 minutes.
The crystallographic structure of the obtained samples was characterized by X-ray diffraction.
The experiments were performed in a symmetrical Bragg-Brentano geometry using Cu Kα radiation.
The patterns were registered in the range from 30° to 80° at 2θ scale.
The crystallographic structure of the deposited CuO coatings is discussed with respect to the
applied technological conditions. The results obtained in the present study are expected to add
knowledge about the processes occurring during reactive magnetron sputtering under different
technological conditions, as well as their influence on structure formation in CuO films.
- PAGES:
81-
- TITLE:
EFFECT OF COOLING RATE ON THE ATOMIC STRUCTURE OF Al75Co25 METALLIC GLASS
- AUTHOR(S):
S. Sengul, U. Domekeli, M. Celtek
- ABSTRACT:
In the present study, the effect of cooling rate on the atomic structure and glass formation
process of Al 75Co25 metallic glass was investigated with a series of classical molecular dynamics
simulations based on the embedded atom method. The effects of the cooling rate on the atomic
structure of the system were discussed in detail using various analysis methods. It has been observed
that the cooling rate has a significant effect on the volume and energy of the system, as well as the
glass transition temperature is lower in the slower cooled system. We observed a splitting in the
second peak of the simulated total (or partial) pair distribution functions, which is a characteristic
behavior for metallic glasses. According to the results of the pair analysis method, 1431 and 1541
bonded pairs were the most dominant pairs at high temperatures, and a significant increase was
observed in 1551 bonded pairs around the glass transition region with decreasing temperature. We
observed that the fraction of them increased when the system was cooled more slowly, indicating that
the cooling rate has a significant effect on the formation of the icosahedral order.
- PAGES:
76-
- TITLE:
COMPARATIVE NEUTRON DIFFRACTION STUDY OF RESIDUAL STRESSES, ARISING AFTER ELECTRON BEAM WELDING OF VARIOUS STEELS
- AUTHOR(S):
D. Kaisheva, G. Bokuchava, I. Papushkin, S. Valkov, M. Ormanova, P. Petrov
- ABSTRACT:
Electron beam welding is a technology in which residual stresses are formed as a result of
temperature gradients. Neutron diffraction method allows the measurement of residual stresses in a
high depth without destruction of the material.
In this report, we present a comparative study of the residual stress distribution at electron beam
welding carried out with approximately the same linear energy of three types of steel. Structural
steel, stainless steel and pressure vessel steel, as well as a sample of welded pure copper and
stainless steel were studied. Minimal residual stresses were obtained in the electron beam welded
pressure vessel steel, which has the lowest coefficient of thermal expansion
- PAGES:
72-
