Subject: Technology
Class: 2A
Program: " elementary School XXI century "author Lutseva E.A.
Topic. Different materials - different properties
Didactic goal: to create conditions for the study of properties different materials that surround a person,
Tasks:
personal
foster love and respect for nature
contribute to the development of experience of joint creative activity of students
metasubject
develop research skills and abilities, the ability to work in pairs; creative thinking of students
subject
find out empirically what properties the materials known to students have: paper, fabric, wood, metal;
Means of education:
multimedia projector, presentation for the lesson
Lutseva, E.A. Class 2 technology. Textbook. - M., Ventana-Graf, 2008
Lutseva, E.A. Workbook "Learning the skill" -M., Ventana-Graf, 2008
samples of materials: pieces of paper, fabric; metal plates. wood
plastic cups with water
Teaching Methods: Research
Forms of organizing cognitive activity:
frontal;
group;
individual.
Stage
Teacher activity
Students' activities
UUD
Self-determination to activity
Guys, in the last lesson we made a doll from different materials. Tell me, could you play with a toy doll made of snow? chocolate? Why?
What did not suit us in these materials?
Tell me, what determines the choice of material for the product?
Today in the lesson we will conduct research and find out what you need to know about the materials in order not to make a mistake in the choice. We will work in groups (5 + 5 + 4)
Children answer that a doll made of snow will melt in the warmth, it will stain hands with chocolate, and it can also deform.
Can you make a nail out of ice? Not
A boat made of sugar? Not
Children express guesses, assumptions.
Personal:
Self-determination (motivation for learning);
regulatory:
goal setting; communicative: planning educational collaboration with teacher and peers
Knowledge update
slide number 2
slide number 3
slide number 4
Frontal work is invited to answer the questions:
What is called a material?
What is called a product?
The correctness of the answer can be checked by clicking on the link on slide No. 3
work with the textbook Read the text on page 21 and answer the questions
Are natural reserves endless?
Material is what something is made of
The product is the creation of human hands
Children read the text on page 21
Telling children about respect for natural resources
communicative: planning educational collaboration with teacher and peers;
cognitive: logical - analysis of objects in order to identify features,
semantic reading.
Setting up educational activities
slide number 5
slides number 6, 7.8
slide number 9
You have the same images on your desk various subjects... Consider the images of objects. What groups can they be divided into? Why? Discuss in pairs. The answers of the children are listened to.
Check the correctness of your actions. What products are made of the same material?
Explain why the materials were used for these products. What are the features? What determines the choice of material for the product?
Children do practical work on dividing objects into groups:
Made of wood: chair, books, board, notebook, wooden gate, dresser
From fabric: curtains, T-shirt, shorts.
Metal: cutlery, drills, iron gates.
Clothing should fit, warm, absorb.
Metal products are durable.
Children make assumptions that they need to know some features, characteristics of materials.
cognitive: logical - analysis of objects in order to identify features and classification; communicative:
proactive cooperation in finding a solution to the problem;
cognitive:general educational self-selection - the formulation of a cognitive goal; brain teaser - formulation of the problem, for which we will investigate
Building a way out of a difficulty
slide number 10.
slide number 11
slide number 14
slide number 15
Let's be curious and explore these materials in more detail.
We are doing research. Group work.
1. Place samples of different materials in front of you: paper, fabric, wood, metal. Consider them carefully. Tell us what you see.
Take each material in your hands, remember, bend. knock. What do you feel?
What you see and feel is the properties of the materials.
In order to understand the features (properties) of materials, we will conduct a practical study, that is, we will study them in detail.
2. Practical study of the properties of various materials. Conduct material properties research. Everything you need to research is on your desks. Enter the research results in the table.
Check the correctness of your work on the sample. Do your answers match the sample. If not, then let's discuss.
Assignment: Do Your Research page 22
1. Acquisition and integration of knowledge - 4
2. Collaboration - 4
3. Communication - 2
4. Problem solving - 3
5. Use of ICT - 1
6. Self-organization and self-regulation - 2
Speaking in oral speech:
Material properties are what you see and feel.
Children conduct research with materials. Study assignment on page 22 of the textbook and fill in the table
Self-test by sample.
regulatory: planning, forecasting; cognitive:
analysis of objects in order to identify features, sign-symbolic actions (work with a table)
communicative- proactive cooperation in the search and selection of information,
plan activities and assign responsibilities;
regulatory: control, assessment, correction;
to carry out a study assignment with self "and mutual check;
cognitive:general educational - the ability to structure knowledge, communicative: partner behavior management - control, correction, assessment of partner actions, skill
adequately interact within the framework of the educational dialogue;
- represent the result of the group's activities.
Primary anchoring
Read the question on page 22
Analyze the table:
Do different materials have similar properties?
Name the same properties for different materials. What material is elastic? And what material with this property do you know?
How does knowing the properties of different materials help each craftsman in his work?
Children work according to the table.
Yes, there are.
Change when deformed: paper, cloth
Does not tear: wood, metal.
Does not deform: wood, metal.
Fabric, rubber.
regulatory: control, assessment, correction; cognitive: the ability to consciously and arbitrarily build a speech utterance, reflection on the methods and conditions of action; communicative: ability to express your thoughts
Assimilation of new knowledge
Creative task in the group
You are given materials. The task is to imagine what can come of them? Think, check with the table, how you can use the properties of the material.
Prove the correctness of the choice of material.
Group work. Children fill out on cards.
Paper -
Wood -
Metal -
Textile -
regulatory: control, correction, highlighting and awareness of what has already been mastered and what else is subject to assimilation, awareness of the quality and level of assimilation;
personal: self-determination
Communicative: the ability to express your thoughts with sufficient completeness and accuracy
Reflection of activity
Guys, now you can answer the question: do different, outwardly dissimilar materials have similar properties?
What new have you learned? What have you learned? Where in life can this knowledge be useful to you?
Which of you found it difficult? Who coped with the difficulties on their own? Whom did the comrades help?
Rate your personal work in the group and the work of the whole group.
Give your opinion about the lesson
Continue the sentences: I didn’t know .... I learned .... I couldn’t…. I learned….
Children's answers.
Communicative: the ability to express your thoughts with sufficient completeness and accuracy; cognitive: reflection; personal: meaning formation
Appendix. Tables.
Material properties
What I'm researching
paper
wood
the cloth
metal
smooth
rough
rough
smooth
loose
dense
loose
dense
Yes
No
Yes
No
Does it stretch (elasticity)
No
No
Yes
No
Yes
No
Yes
No
Yes
Yes, but does not sink
Yes
No, drowning
Yes
No
Yes
No
Material properties
What I'm researching
paper
wood
the cloth
metal
What surface (smooth, rough)
What is the density (dense, loose)
Does it change when creased (deformation)
Does it stretch (elasticity)
What transparency (translucent or not)
What is the relationship to moisture (gets wet or not)
What is the strength (breaks or not)
Home> Lecture
General information O building materials.
In the process of construction, operation and repair of buildings and structures, building products and structures from which they are erected are subjected to various physical and mechanical, physical and technological influences. A hydraulic engineer is required to competently select the right material, product or structure that has sufficient strength, reliability and durability for specific conditions.
LECTURE No. 1
General information about building materials and their main properties.
Building materials and products used in the construction, reconstruction and repair of various buildings and structures are divided into natural and artificial, which in turn are divided into two main categories: the first category includes: brick, concrete, cement, timber, etc. They are used when erecting various elements of buildings (walls, ceilings, coatings, floors). To the second category - special purpose: waterproofing, thermal insulation, acoustic, etc. The main types of building materials and products are: natural stone building materials from them; binders inorganic and organic; forest materials and products from them; hardware. Depending on the purpose, construction conditions and operation of buildings and structures, appropriate building materials are selected that have certain qualities and protective properties from the impact on them of a different external environment. Given these features, any building material must have certain building and technical properties. For example, the material for the outer walls of buildings should have the lowest thermal conductivity with sufficient strength to protect the room from the outside cold; the material of the structure for irrigation and drainage purposes - watertightness and resistance to alternating moisture and drying; material for covering expensive (asphalt, concrete) must have sufficient strength and low abrasion to withstand traffic loads. When classifying materials and products, it must be remembered that they must have good properties and qualities.Property- the characteristic of the material, manifested in the process of its processing, application or operation. Quality- a set of material properties that determine its ability to meet certain requirements in accordance with its purpose. The properties of building materials and products are classified into three main groups: physical, mechanical, chemical, technological and etc . TO chemical include the ability of materials to resist the action of a chemically aggressive environment, causing exchange reactions in them leading to the destruction of materials, a change in their initial properties: solubility, corrosion resistance, resistance to decay, hardening. Physical properties : average, bulk, true and relative density; porosity, moisture, moisture yield, thermal conductivity. Mechanical properties: ultimate strength in compression, tensile, bending, shear, elasticity, plasticity, stiffness, hardness. Technological properties: workability, heat resistance, melting, speed of hardening and drying.
Physical and Chemical properties materials.
Average densityρ 0 mass m unit volume V 1 completely dry material in its natural state; it is expressed in g / cm 3, kg / l, kg / m 3. Bulk density bulk materials ρ n mass m unit volume V n dried loose material; it is expressed in g / cm 3, kg / l, kg / m 3. True densityρ mass m unit volume V material in an absolutely dense state; it is expressed in g / cm 3, kg / l, kg / m 3. Relative densityρ(%) - the degree of filling the volume of the material with a solid substance; it is characterized by the ratio of the total volume of solid matter V in the material to the entire volume of the material V 1 or the ratio of the average density of the material ρ 0 to its true density ρ:, or
. PorosityP
- the degree of filling the volume of the material with pores, voids, gas-air inclusions: for solid materials: 
, for bulk: 
Hygroscopicity- the ability of the material to absorb moisture from the environment and thicken it in the mass of the material. HumidityW
(%)
- the ratio of the mass of water in the material m v =
m 1
-
m
to its mass in an absolutely dry state m: 
Water absorptionV
- characterizes the ability of the material in contact with water to absorb and retain it in its mass. Distinguish between mass V m and volumetric V O water absorption. Mass water absorption(%)
- the ratio of the mass of water absorbed by the material m v to the mass of material in an absolutely dry state m: 
Volumetric water absorption(%)
- the ratio of the volume of water absorbed by the material m v /
ρ
v
to its volume in a water-saturated state V 2
: 
Moisture yield- the ability of the material to give off moisture. Mechanical properties of materials.
Compressive strengthR - breaking load ratio P (H) to the cross-sectional area of the sample F(cm 2). It depends on the size of the sample, the rate of application of the load, the shape of the sample, and humidity. Tensile strengthR R - breaking load ratio R to the original cross-sectional area of the sample F. Flexural strengthR and - determined on specially made beams. Rigidity- the property of the material to give small elastic deformations. Hardness- the ability of a material (metal, concrete, wood) to resist the penetration of a steel ball into it under a constant load.LECTURE No. 2
Natural stone materials.
Classification and main types rocks.
Rocks that have the necessary building properties are used as natural stone materials in construction. According to geological classification, rocks are divided into three types: 1) igneous (primary), 2) sedimentary (secondary) and 3) metamorphic (modified). 1) Igneous (primary) rocks formed during the cooling of molten magma that rose from the depths of the earth. The structure and properties of igneous rocks largely depend on the cooling conditions of the magma, and therefore these rocks are subdivided into deep and poured out. Deep rocks formed during the slow cooling of magma in the depths crust at high pressures of the overlying layers of the earth, which contributed to the formation of rocks with a dense granular-crystalline structure, high and medium density, high compressive strength. These rocks have low water absorption and high frost resistance. These rocks include granite, syenite, diorite, gabbro, etc. Effused rocks formed during the release of magma to earth surface with relatively fast and uneven cooling. The most common erupted rocks are porphyry, diabase, basalt, volcanic loose rocks. 2) Sedimentary (secondary) rocks formed from primary (igneous) rocks under the influence of temperature extremes, solar radiation, the action of water, atmospheric gases, etc. In this regard, sedimentary rocks are subdivided into detrital (loose), chemical and organogenic. To the debris loose rocks include gravel, crushed stone, sand, clay. Chemical sedimentary rocks : limestone, dolomite, gypsum. Organogenic rocks: limestone-shell rock, diatomite, chalk. 3) Metamorphic (modified) rocks formed from igneous and sedimentary rocks under the influence of high temperatures and pressures in the process of raising and lowering the earth's crust. These include shale, marble, quartzite.
Classification and main types of natural stone materials.
Natural stone materials and products are obtained by processing rocks. By way of receiving stone materials are subdivided into torn stone (quarry) - they are mined by explosive method; roughly chipped stone - obtained by splitting without processing; crushed - obtained by crushing (crushed stone, artificial sand); sorted stone (cobblestone, gravel) .Stone materials are divided into stones by shape irregular shape(crushed stone, gravel) and piece products that have the correct shape (slabs, blocks). Crushed stone- acute-angled pieces of rocks ranging in size from 5 to 70 mm, obtained by mechanical or natural crushing of rubble (torn stone) or natural stones. It is used as a coarse aggregate for the preparation of concrete mixtures, foundation devices. Gravel- rounded pieces of rocks ranging in size from 5 to 120 mm, also used for the preparation of artificial gravel and crushed stone mixtures. - loose mixture of grains of rocks from 0.14 to 5 mm in size. It is usually formed as a result of weathering of rocks, but it can also be obtained artificially - by crushing gravel, crushed stone, and pieces of rocks.LECTURE No. 3
Hydrotational (inorganic) binders.
- Airborne binders. Hydraulic binders.
Hydraulic lime is a slow setting and slow hardening substance. It is used for the preparation of mortars, low-grade concretes, lightweight concretes, and for the production of mixed concretes. Portland cement- a hydraulic binder obtained by joint, fine grinding of clinker and gypsum dihydrate. Clinker- a product of firing before sintering (at t> 1480 ° C) of a homogeneous, definite composition of natural or raw limestone or gypsum mixture. The raw material is fired in rotary kilns. Portland cement is used as a binder in the preparation of cement mortars and concretes. Slag Portland cement- in its composition has a hydraulic additive in the form of granular, blast-furnace or electrothermophosphoric slag., cooled according to a special mode. It is obtained by joint grinding of Portland cement clinker (up to 3.5%), slag (20 ... 80%), and gypsum stone (up to 3.5%). Slag Portland cement has a slow increase in strength in the initial periods of hardening, but later the rate of strength growth increases. It is sensitive to ambient temperature, resistant when exposed to soft sulfate waters, has a reduced frost resistance. Portland carbonate cement are obtained by joint grinding of cement clinker with 30% limestone. It has a reduced heat generation during hardening, increased durability.
LECTURE No. 4
Building solutions.
General information.
Building mortars are carefully dosed fine-grained mixtures consisting of an inorganic binder (cement, lime, gypsum, clay), fine aggregate (sand, crushed slag), water and, if necessary, additives (inorganic or organic). When freshly prepared, they can be laid on the base thin layer filling in all its irregularities. They do not exfoliate, set, harden and gain strength, turning into a stone-like material. Mortars are used for masonry, finishing, repair and other works. They are classified by medium density: heavy with medium ρ = 1500kg / m 3, light to medium ρ <1500кг/м 3 . По назначению: гидроизоляционные, талтопогенные, инъекционные, кладочные, отделочные и др. Растворы приготовленные на одном виде вяжущего вещества, называют простыми, из нескольких вяжущих веществ смешанными (цементно-известковый). Строительные растворы приготовленные на воздушных вяжущих, называют воздушными (глиняные, известковые, гипсовые). Состав растворов выражают двумя (простые 1:4) или тремя (смешанные 1:0,5:4) числами, показывающие объёмное соотношение количества вяжущего и мелкого заполнителя. В смешанных растворах первое число выражает объёмную часть основного вяжущего вещества, второе – объёмную часть дополнительного вяжущего вещества по отношению к основному. В зависимости от количества вяжущего вещества и мелкого заполнителя растворные смеси подразделяют на fatty- containing a large amount of astringent. Normal- with the usual binder content. Skinny- containing a relatively small amount of astringent (low plastic). For the preparation of mortars, it is better to use sand with grains that have a rough surface. Sand protects the solution from cracking during hardening, and reduces its cost. Waterproofing mortars (waterproof)- cement mortars of the composition 1: 1 - 1: 3.5 (usually fatty), to which ceresite, sodium amominate, calcium nitrate, ferric chloride, bitumen emulsion are added. Ceresite- represents a mass of white or yellow color, obtained from anilic acid, lime, ammonia. Ceresite fills small pores, increases the density of the solution, making it waterproof. For the manufacture of waterproofing mortars, Portland cement, sulfate-resistant Portland cement are used. Sand is used as a fine aggregate in waterproofing solutions. Masonry mortars- used when laying stone walls, underground structures. They are cement-lime, cement-clay, lime and cement. Finishing (plastering) solutions- subdivided by purpose into external and internal, by location in the plaster into preparatory and finishing. Acoustic solutions- light mortars with good sound insulation. These solutions are prepared from Portland cement, Portland slag cement, lime, gypsum, and other binders using lightweight porous materials (pumice, perlite, expanded clay, slag) as a filler.LECTURE No. 5
Conventional concrete based on hydration binders.
- Materials for normal (warm) concrete. Composition design concrete mix.
In addition to partial remains, complete remains are found A, which are defined as the sum of all private residuals in% on the overlying sieves + partial remainders on a given sieve:
According to the results of sand sifting, its size modulus is determined:
where A- total remnants on sieves,%. Coarse sand ( M To >2,5
), average ( M To =2,5…2,0
), small ( M To =2,0…1,5
), very small ( M To =1,5…1,0
). By plotting the sand sifting curve on the graph of the permissible grain size composition, the suitability of the sand for the production of concrete mixture is determined. 1- laboratory sieving curve for sand and coarse aggregate, respectively. Great value in the selection of sand for a concrete mixture has its intergranular voidness V P (%)
, which is determined by the formula: ρ
n.p- bulk density of sand, g / cm 3; ρ
- true density of sand, g / cm 3; V good sands intergranular voidness is 30 ... 38%, in different-grained voids - 40 ... 42%. Large placeholder... Natural or artificial crushed stone or gravel with a grain size of 5 to 70 mm is used as a coarse aggregate for a concrete mixture. To ensure an optimal grain size composition, the coarse aggregate is divided into fractions depending on the largest grain size. D naib.; At D naib= 20mm coarse aggregate has two fractions: from 5 to 10 mm and from 10 to 20 mm; At D naib= 40mm - three fractions: from 5 to 10 mm; from 10 to 20 mm and from 20 to 40 mm; At D naib= 70mm - four fractions: from 5 to 10 mm; from 10 to 20 mm; from 20 to 40 mm; from 40 to 70 mm. The intergranular voidness of the coarse aggregate has a great influence on the consumption of cement during the preparation of the concrete mixture. V p.cr (%),
which is determined with an accuracy of 0.01% by the formula: ρ
n.cr Is the average bulk density of the coarse aggregate. ρ
because the bite- average density of coarse aggregate in a piece. The intergranular voidness index should be minimal. Its lower value can be obtained by selecting the optimal grain size composition of the coarse aggregate. The grain size composition of the coarse aggregate is established as a result of sifting the dried coarse aggregate with a set of sieves with holes of size 70; 40; twenty; 10; 5 mm, taking into account its maximum D naib and minimal D naim size. Crushed stone- usually artificial loose material with non-rounded rough grains, obtained by crushing rocks, coarse natural gravel or artificial stones. To determine the suitability of crushed stone, you need to know: the true density of the rock, the average density of crushed stone, the average bulk density of crushed stone, the relative intergranular voidness and moisture content of crushed stone Gravel- loose natural material with rounded, smooth grains, formed in the process of physical weathering of rocks. The requirements for gravel are the same as for crushed stone. Additives... The introduction of additives into cement, mortar or concrete mixture is simple and in a convenient way improving the quality of cement, mortar and concrete. Allowing to significantly improve not only their properties but also technical and operational indicators. Additives are used in the production of binders, the preparation of mortars and concrete mixtures. They allow you to change the quality of the concrete mix and the concrete itself; affecting workability, mechanical strength, frost resistance, crack resistance, water resistance, water resistance, thermal conductivity, environmental resistance. The main properties of the concrete mix include cohesion (the ability to maintain its homogeneity without delaminating during transportation, unloading), uniformity, water-holding capacity (plays a significant role in the formation of the structure of concrete, acquiring its strength, water resistance and frost resistance), workability (its ability to quickly minimum cost energy to acquire the required configuration and density, ensuring the production of high-density concrete). The freshly prepared concrete mixture must be well mixed (homogeneous), suitable for transportation to the place of installation, taking into account the weather conditions, while resisting water separation and delamination. The task of designing and selecting the composition of the concrete mix includes the selection of the necessary materials (binder and other components) and the establishment of their optimal quantitative ratio. On the basis of this, a concrete mixture with specified technological properties is obtained, as well as the most economical and durable concrete that meets design and operational requirements with the lowest possible cement consumption. Consequently, the concrete mixture of the designed composition must have non-segregation, the necessary workability, cohesion, and the concrete made from this mixture must have the required properties: density, strength, frost resistance, and water resistance. The simplest way to design the composition of the concrete mix is to calculate in absolute volumes, based on the assumption that the prepared, laid and compacted concrete mix should not have voids. The design of the composition is carried out using the current recommendations and normative documents in the following sequence: And the concrete yield ratio:
Concrete yield ratio β should be in the range of 0.55 ... 0.75. The projected composition of the concrete mixture is specified on trial mixes. They also check the mobility of the concrete mixture. If the mobility of the concrete mixture turns out to be more than required, then water and cement are added to the batch in small portions, while maintaining a constant ratio V / C until the mobility of the concrete mixture becomes equal to the specified one. If the mobility turns out to be more than the specified one, then sand and coarse aggregate are added to it (in portions of 5% of the initial amount), keeping the selected ratio V / C... Based on the results of test batching, adjustments are made to the projected composition of the concrete mixture, given that in production conditions the sand and coarse aggregate used are in a wet state, and the coarse aggregate has some water absorption, consumption ( l Document
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Dissertation abstractIntroduction
Dear students, we are starting to study the course "General Materials Science". The lectures that will be given during this semester will help you understand the physicochemical nature of the structure and properties of various materials. You will learn why natural and artificially created materials have different thermal conductivity, mechanical and operational properties, how these properties are related to each other, how and within what limits they can be changed. Simultaneously with the study of these issues, you will become more deeply acquainted with the physical and chemical properties of the elements, information about which is laid down in the periodic system of D.I. Mendeleev. I would like to emphasize that the structure of atoms of chemical elements determines the structure and energy of the chemical bonds formed by them, which, in turn, underlie the entire complex of properties of substances and materials. Only by relying on an understanding of the chemical interaction of atoms, it is possible to control the processes occurring in substances, and to obtain the specified performance characteristics.
However, more important than the study of individual problems outlined in the lectures is the opportunity given to you to combine the basic provisions of physics, chemistry and applied scientific directions (thermophysics, mechanics) for a comprehensive understanding of the interaction of substances and their properties.
In the lectures, the main attention is paid to the fundamental foundations of materials science due to the fact that modern materials science is aimed at obtaining materials with given characteristics and serves as the basis for science-intensive technologies of the 21st century.
Material is called a substance that has the necessarya set of properties to perform a given function separatelyor in combination with other substances.
Modern materials science fully developed as a science in the second half of the 20th century, which was associated with the rapid growth of the role of materials in the development of engineering, technology and construction. The creation of fundamentally new materials with given properties, and on their basis, the most complex structures allowed mankind to achieve unprecedented success in atomic and space technology, electronics, information technology, construction, etc. in a short time. We can assume that Materials Science - this section scientific knowledge devoted to the properties of substances and their directional change in order to obtain materials with predetermined performance characteristics. It is based on the fundamental basis of all branches of physics, chemistry, mechanics and related disciplines and includes the theoretical foundations of modern science-intensive technologies for the production, processing and use of materials. The basis of materials science is knowledge about the processes occurring in materials under the influence of various factors, about their influence on the complex of material properties, about methods of monitoring and controlling them. Therefore, materials science and materials technology are interrelated areas of knowledge.
The course in materials science and technology of building materials serves goals knowledge of the nature and properties of materials, methods of obtaining materials with specified characteristics for the most effective use in construction.
Main tasks studying the course:
To give an understanding of the physicochemical nature of the phenomena that occur in materials when they are exposed to various factors in the conditions of production and operation, and their influence on the properties of materials;
Establish the relationship between the chemical composition, structure and properties of materials;
To study the theoretical foundations and practice of implementing various methods of obtaining and processing materials that ensure high reliability and durability of building structures;
To give knowledge about the main groups of non-metallic materials, their properties and applications.
The lectures reveal:
The fundamentals of the interaction of atoms and molecules, which make it possible to further explain the effect on the properties of a material of its chemical composition and processes of directed processing;
Solid structure, crystal structure defects and their role in the formation of material properties;
Phenomena of heat, mass and charge transfer, which are the essence of any technological process;
Theoretical foundations for obtaining amorphous structures of materials;
Elements of the mechanics of elastic and plastic deformation and destruction of material, which underlie the formation of strength and reliability of modern building materials and structures, as well as methods of their testing;
So, the task of modern materials science is to obtain materials with predetermined properties. The properties of materials are determined by the chemical composition and structure, which are the result of obtaining the material and its further processing. The development of materials and technologies requires knowledge of the physical and chemical phenomena and processes occurring in the material at various stages of its production, processing and operation, their prediction, description and control. Thus, knowledge of the theory is necessary to create controlled technological processes, the result of which will be a material with clearly defined values of working properties.
The physicochemical properties of a substance are determined by the electronic structure of its atoms. The interactions of atoms are associated, first of all, with the interaction of their electronic shells. Therefore, when developing materials and processes for their preparation, it is necessary to clearly understand how various chemical elements give and receive electrons, how a change in the electronic state affects the properties of elements.
Let's remember electronic structure of the atom.
Electronic structure of the atom
For about two and a half thousand years, the ancient Greek philosopher Democritus expressed the idea that all bodies around us consist of the smallest invisible and indivisible particles - atoms.
From atoms, as from peculiar bricks, molecules are assembled: from identical atoms - molecules simple, substances, from atoms of various types - molecules complex substances.
Already at the end of the nineteenth century, science established that atoms are not "indivisible" particles, as the ancient philosophy imagined, but, in turn, consist of even smaller and, so to speak, even simpler particles. At present, the existence of about three hundred elementary particles that make up atoms has been proven with greater or less certainty.
To study chemical transformations, in most cases, it is enough for us to indicate three particles that make up an atom: proton, electron andneutron.
A proton is a particle of mass conventionally taken as a unit (1/12 of the mass of a carbon atom) and a unit positive charge. Proton mass - 1.67252 x 10 -27 kg
An electron is a particle with practically zero mass (1836 times less than that of a proton) and a single negative charge. The mass of an electron is 9.1091x10 -31 kg.
A neutron is a particle with a mass almost equal to the mass of a proton, but having no charge (neutral). The mass of the neutron is 1.67474 x 10 -27 kg.
Modern science presents the atom with approximately the same structure as our solar system: in the center of the atom is core(the sun), around which electrons revolve at a relatively large distance (like planets around the sun). This "planetary" model of the atom, proposed in 1911 by Ernest Rutherford and refined by Bohr's postulates in 1913, has retained its significance to the present day.
In the nucleus, consisting of protons and neutrons and occupying a very small part of the volume of an atom, the bulk of the atom is concentrated (the mass of electrons is usually not taken into account in chemical calculations of atomic and molecular masses).
The number of protons in the nucleus determines view atom. In total, more than a hundred types of atoms have now been discovered, which are presented in the Table of elements under numbers corresponding to the number of protons in the nucleus.
The simplest atom contains only one proton in its nucleus: this is a hydrogen atom. The more complex atom of helium already has two protons in its nucleus, the third (lithium) has three, etc. A particular kind of atom is called an element.
2. The structure and properties of finishing materials
Internal structure of materials
Depending on the state of aggregation and stability, solids can have a strictly ordered structure - crystalline, or disordered, chaotic structure - amorphous.
The nature of the particles located at the sites of the crystal lattice and the prevailing forces of interaction (chemical bonds) determine the nature of the crystal lattice: atomic with covalent bonds, molecular with van der Waals and hydrogen bonds, ionic with ionic bonds, metallic with metal bonds.
Atomic lattice consists of neutral atoms linked by covalent bonds. Substances with covalent bonds are distinguished by high hardness, refractoriness, insolubility in water and in most other solvents. Diamond and graphite are examples of atomic lattices. The energy of covalent bonds is from 600 to 1000 kJ / mol
Molecular lattice built of their molecules (I 2, Cl 2, CO 2, etc.) linked to each other by intermolecular or hydrogen bonds. Intermolecular bonds have a low energy value, no more than 10 kJ / mol; hydrogen bonds have a somewhat greater value (20-80 kJ / mol), therefore substances with a molecular lattice have low strength, low melting point, and high volatility. Such substances do not conduct current. Substances with a molecular lattice include organic materials, noble gases, and some inorganic substances.
Ionic lattice formed by atoms that are very different in electronegativity. It is typical for compounds of alkali and alkaline earth metals with halogens. Ionic crystals can also consist of polyatomic ions (for example, phosphates, sulfates, etc.). In such a lattice, each ion is surrounded by a certain number of its counterions. For example, in the NaCl crystal lattice, each sodium ion is surrounded by six chlorine ions, and each chlorine ion is surrounded by six sodium ions. Due to the non-directionality and unsaturation of the ionic bond, the crystal can be regarded as a giant molecule, and the usual concept of a molecule here loses its meaning. Substances with an ionic lattice are characterized by a high melting point, low volatility, high strength and significant energy of the crystal lattice. These properties bring ionic crystals closer to atomic ones. The binding energy of the ionic lattice is approximately equal, according to some sources, less than the energy of the covalent lattice.
Metal grilles form metals. The lattice sites contain metal ions, and the valence electrons are delocalized throughout the crystal. Such crystals can be considered as one huge molecule with a single system of multicenter molecular orbitals. The electrons are in the bonding orbitals of the system, and the antibonding orbitals form the conduction band. Since the binding energy of the bonding and antibonding orbitals is close, electrons easily pass into the conduction band and move within the crystal, forming, as it were, an electron gas. Table 3.1 as an example, the binding energies for crystals with different types communication.
The ordered arrangement of particles in the crystal is retained at large distances, and in the case of ideally formed crystals, throughout the entire volume of the material. This ordering of the structure of solids is called long-range order.
Material classification
Solid materials are generally classified into three main groups. These are metals, ceramics and polymers. This division is based primarily on the features of the chemical structure and atomic structure of matter. Most of the materials can be quite unambiguously attributed to one group or another, although intermediate cases are also possible. In addition, it should be noted the existence of composites in which materials belonging to two or three of the listed groups are combined. Below will be a brief description of the various types of materials and their comparative characteristics.
Another type of materials are modern special (advanced) materials intended for use in high-tech (high-tech) areas such as semiconductors, biological materials, smart materials and substances used in nanotechnology.
METALS
Materials belonging to this group include one or more metals (such as iron, aluminum, copper, titanium, gold, nickel), as well as often some non-metallic elements (such as carbon, nitrogen or oxygen) in relatively small quantities.
The atoms in metals and alloys are arranged in a very perfect order. In addition, compared to ceramics and polymeric materials, the density of metals is relatively high.
In terms of mechanical properties, all of these materials are relatively tough and durable. In addition, they have a certain ductility (i.e., the ability to deform large without destruction), and resistance to fracture, which ensured their wide application in a variety of structures.
V metal materials there are many delocalized electrons, that is, electrons not associated with specific atoms. It is the presence of such electrons that directly explains many of the properties of metals. For example, metals are extremely good conductors for electrical current and heat. They are impervious to visible light. Polished metal surfaces are shiny. In addition, some metals (eg iron, cobalt and nickel) have desirable magnetic properties for their use.
CERAMICS
Ceramics is a group of materials that occupy an intermediate position between metals and non-metallic elements. How general rule, the class of ceramics includes oxides, nitrides and carbides. For example, some of the most popular types of ceramics are composed of aluminum oxide (Al2O3), silicon dioxide (SiO2), silicon nitride (Si3N4). In addition, among those substances that many call traditional ceramic materials include various clays (in particular, those used to make porcelain), as well as concrete and glass. In terms of mechanical properties, ceramics are relatively tough and durable materials comparable in these characteristics to metals. In addition, typical ceramics are very hard. However, ceramics are extremely brittle material (almost complete lack of ductility) and do not resist fracture well. All typical ceramics do not conduct heat and electricity (i.e. their electrical conductivity is very low).
Ceramics are characterized by higher resistance to high temperatures and harmful environmental influences. As for their optical properties, ceramics can be transparent, translucent or completely opaque materials, and some oxides, for example, iron oxide (Fe2O3), have magnetic properties.
COMPOSITES
Composites are a combination of two (or more) separate materials belonging to the different classes of substances listed above, i.e. metals, ceramics and polymers. The goal of creating composites was to achieve such a combination of properties of various materials that cannot be obtained for individual components, as well as to provide an optimal combination of their characteristics. A large number of different composites are known, which are obtained by combining metals, ceramics and polymers. Moreover, some natural materials are also composites, such as wood and bone. However, most of the composites discussed in this book are materials made from synthetic materials.
One of the most popular and familiar to all composite materials is fiberglass. This material is short glass fibers embedded in a polymer matrix, usually epoxy or polyester resin. Glass fibers are strong and tough, but fragile. At the same time, the polymer matrix is plastic, but its strength is low. The combination of these substances leads to obtaining a relatively rigid and high-strength material, which, nevertheless, has sufficient ductility and flexibility.
Another example of a technologically important composite is carbon fiber reinforced plastics (CFRPs). In these materials, carbon fibers are placed in a polymer matrix. Materials of this type are stiffer and more durable than fiberglass, but at the same time they are more expensive. CFRPs are used in aerospace and high-quality sports equipment such as bicycles, golf clubs, tennis rackets, skis and snowboards.
ADVANCED MATERIALS
Materials that are intended for use in high-tech products ("high-tech") are sometimes conventionally referred to as "progressive" materials. High technology usually refers to devices or products that are based on sophisticated modern principles. These products include a variety of electronic equipment such as digital video and audio cameras, CD / DVD players, computers, fiber optic systems, as well as space satellites, aerospace and rocket technology.
Progressive materials, in essence, are usually typical of the materials discussed above, but with improved properties, but also new materials with outstanding characteristics. These materials can be metals, ceramics or polymers, but their cost is usually very high. Progressive materials also include semiconductors, biomaterials and substances that we call "materials of the future." These are the so-called "smart" materials and nanotechnology products, which are intended, for example, for the manufacture of lasers, integrated circuits, magnetic storage devices, liquid crystal displays and optical fibers.
SEMICONDUCTORS
In terms of electrical properties, semiconductors occupy an intermediate position between electrically conductive materials (metals and metal alloys) and insulators (ceramics and polymers). In addition, the electrical characteristics of semiconductors are extremely sensitive to the presence of minimal amounts of foreign atoms, the concentration of which must be controlled down to the level of very small regions. The development of semiconductor materials made possible the development of integrated systems that have revolutionized electronics and computer technology (even if not to mention the changes in our lives) over the past three decades.
BIOMATERIALS
Biomaterials are used to create implants for the human body, which are designed to replace diseased or destroyed organs or tissues. Materials of this type should not emit toxic substances and should be compatible with human tissues (i.e. should not cause rejection reactions). All of these types of substances - metals, ceramics, polymers, and semiconductors - can be used as biomaterials. Some biomaterials that are used to make artificial hip joints can be cited as an example.
FUTURE MATERIALS
“Smart” (or intelligent) materials is a group of new artificially developed substances that have a significant impact on many modern technologies. The definition of "smart" means that these materials are able to sense changes in the environment and respond to these changes in a predetermined way - a quality inherent in living organisms. The concept of smart materials has also been extended to complex systems built from both smart and traditional substances.
Some types of sensors (recognizing incoming signals), as well as executive systems (activators) that play the role of responsive and adaptive devices, can be used as components of smart materials (or systems). The latter can be used to change the shape, position, natural frequencies or mechanical characteristics in response to changes in temperature, light intensity, electric or magnetic field strength.
Four types of materials are commonly used as activators: shape memory alloys, piezoelectric ceramics, magnetostrictive materials, and electrorheological / electromagnetic fluids.
Memory alloys are metals that, after deformation, return to their original shape if the temperature changes.
Piezoelectric ceramics expand and contract in response to changes in the electric field (or voltage); if their sizes change, then this leads to the excitation of an electrical signal. The behavior of magnetostrictive materials is similar to the reaction of piezoelectrics, but only as a reaction to a change magnetic field... As for electro- and magnetorheological fluids, these are media that undergo huge changes in viscosity in response to changes in the electric or magnetic field, respectively.
Materials / devices used as sensors can be optical fibers, piezoelectrics (some polymers include) and microelectromechanical devices, abbreviated as MEMS.
An example of smart devices is a system used in helicopters to reduce cabin noise generated by rotating blades. Piezoelectric sensors built into the blades monitor stresses and strains; the signal is transmitted from these sensors to the actuator, which, with the help of a computer, generates an “anti-noise” that dampens the sound from the operation of the helicopter propellers.
NANOTECHNOLOGICAL MATERIALS
Until very recently, the generally accepted procedure for work in the field of chemistry and physics of materials was that at first very large and complex structures were studied, and then research moved to the analysis of the smaller fundamental blocks that make up these structures. This approach has sometimes been called top-down. However, with the development of scanning microscopy technology, which made it possible to observe individual atoms and molecules, it became possible to manipulate atoms and molecules in order to create new structures, and thereby obtain new materials that are built on the basis of elements of atomic size (the so-called "material design "). These possibilities of accurately collecting atoms opened up prospects for creating materials with mechanical, electrical, magnetic and other properties that would have been unattainable using other methods. We will call this approach “bottom-up”, and nanotechnology is studying the properties of such new materials, where the prefix “nano” means that the dimensions of the structural elements are on the order of a nanometer (ie, 10–9 m). Usually, it comes about structural elements with dimensions less than 100 nm, which is equivalent to about 500 atomic diameters.
One example of this type of material is carbon nanotubes. In the future, we will undoubtedly be able to find more and more areas in which the merits of nanotechnology materials will manifest themselves.
THE NEED TO CREATE NEW MATERIALS
While tremendous progress has been made in materials science and materials technology over the past few years, there remains a need to develop even better and more specialized materials and to assess the relationship between the production of such materials and its impact on the environment. Some comments are needed on this issue to outline possible perspectives in this area.
Nuclear power offers some promises for the future, but many challenges remain in the development of new materials that are needed at all stages - from the fuel placement system in a reactor to the storage of radioactive waste.
Large energy costs are associated with transportation. Reducing the weight of transport devices (cars, airplanes, trains, etc.), as well as increasing the temperature at which the engines operate, will contribute to more efficient energy use. This requires the creation of high-strength, lightweight engineering materials, as well as materials that can operate at elevated temperatures.
Further, there is a recognized need for new, economically viable energy sources, as well as more efficient use of existing sources. Undoubtedly, materials with the required characteristics play a huge role in the development of this direction. For example, the possibility of direct conversion of solar energy into electric current has been demonstrated. Currently, solar cells are quite complex and expensive devices. Undoubtedly, new relatively cheap technological materials should be created, which should be more efficient in the implementation of the use of solar energy.
Another very attractive and very real example in energy conversion technology is hydrogen fuel cells, which also have the advantage of not polluting the environment. The use of this technology in electronic devices is just beginning; in the future, such elements can be used as power plants in cars. New materials are needed to create more efficient fuel cells, and new catalysts are needed to produce hydrogen.
To maintain the quality of the environment at the required level, we need to control the composition of air and water. Various materials are used to control contamination. In addition, there is a need to improve the recycling and purification methods of materials in order to reduce environmental pollution, i.e. the task is to create less waste and less harm to the environment around us in the extraction of minerals. It should also be taken into account that toxic substances are generated during the production of some materials, so the possible environmental damage from the dumping of such waste should be taken into account.
Many of the materials we use come from irreplaceable resources, i.e. sources that cannot be regenerated. This applies, for example, to polymers, for which the primary feedstock is oil, and to some metals. These irreplaceable resources are gradually being depleted. Hence the need arises: 1) to discover new sources of these resources; 2) creation of new materials with properties similar to existing ones, but less damaging to the environment; 3) strengthening the role of recycling processes and, in particular, the development of new technologies that allow for recycling. As a consequence of all this, the need arises economic assessment not only production, but also taking into account environmental factors, so it turns out to be necessary to analyze the entire life cycle of the material - "from cradle to grave" - and the production process as a whole.
Casting is a method of manufacturing a workpiece or product by filling a cavity of a given configuration with liquid metal, followed by its solidification. The workpiece or product obtained by casting is called casting.
Foundry- the main procurement base for all areas of mechanical engineering. In many cases, casting is the only possible way to obtain workpieces with complex shapes: Cast billets are the cheapest and often have the smallest machining allowance.
Casting in shell forms.
The casting mold here is a shell with a thickness of 6-10 mm, made of a refractory base material (filler) and a synthetic resin as a binder. The principle of obtaining shells is based on the properties of a binder material that can irreversibly cure when heated. They are widely used as a refractory base quartz sand... The binder is phenol-formaldehyde synthetic thermosetting resins. By casting into shell molds, castings of increased accuracy are obtained, with a better surface quality than when casting into sand molds. The process is extremely productive and easy to mechanize.
List of used literature
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Vishnevetskiy Yu.T. Materials Science for Technical Colleges: A Textbook. - M .: Dashkov and Co, 2008.
Zaplatin V.N. Reference manual for materials science (metalworking): Textbook. manual for NGOs. - M .: Academy, 2007.
Materials Science: Textbook for Universities. / Ed. Arzamasova B.N. - M .: MGTU im. Bauman, 2008.
Materials science: Textbook for open source software. / Adaskin A.M. and others. Ed. Solomentseva Yu.M. - M .: Higher. shk., 2006.
Materials science: Textbook for open source software. / Ed. Batienko V.T. - M .: Infra-M, 2006.
Moryakov O.S. Materials science: Textbook for open source software. - M .: Academy, 2008.
Fundamentals of materials science (metalworking): Textbook. manual for NGOs. / Zaplatin V.N. - M .: Academy, 2008.