Khibiny. First, it should be said about apatite-nepheline ores. Today, their deposits have been established, these are Kukisvumchorr, Yukspor, Rasvumchorr, Koashva, Partomchorr, Kuelpor, Lyavoyok, Deer Creek, Nyorkpakhk, Suoluyyiv, Poachvumchorr, Valleepahk, Eveslogchorr. Being a mineral, apatite can have a different range of shades. As a rule, starting from white and ending with green, but black apatites are also found in nature.

Mineral fertilizers are made from apatite, the most famous and often used is superphosphate. It is obtained by treating apatite concentrate with sulfuric acid. But meanwhile, phosphoric anhydride contained in apatite takes a completely different form, it turns out to be easily soluble, which is why it is perfectly perceived by plants.

Moreover, nepheline is also extracted from the apatite concentrate, which subsequently becomes the product from which potash, soda, and much more are made. Then this fossil will be used in more than twenty industries. Its content in the ore varies from 5 to 50 percent. The composition of apatite and nepheline in the ore is interconnected, that is, if apatite predominates in it, then there will be much less nepheline, and vice versa, if there is more nepheline in the ore, this means that there will be much less apatite.

Usually, apatite-nepheline ore contains sphen-mineral, it consists of silicon, titanium oxide, tantalum, niobium and sodium. Solid titanium white is made from it, very durable and reliable. On top of that - metallic titanium, which does not corrode, is not afraid of alkali and other acids, and is very light. The Yukspora rock is considered to be the richest mineral.

A peculiar characteristic of the Khibiny mountain range can be considered a ring structure. The mountains that make up the array are arcs that are literally nested into each other.

The landscape of the Khibinites organizes a partial ring of the Khibiny mountain range. Aegirine, nepheline and potassium feldspar dominate as minerals. Rocks are distinguished by the presence of a number of ores, such as titanium, zirconium, molybdenum and rare soil containing cerium and yttrium.

The second complex of rischorrites looks like a massive, gray, with a hint of green rock.

And it contains crystals of feldspar and nepheline, as well as a mixture of colored minerals from aegirine-augite, mica, astrophyllite, enigmatite, sphene, lamprophyllite.

The latter is called ijolite-urtites, it differs greatly from other rocks due to the chemical component. It exceeds the level of alkali and alumina, and also greatly reduces the level of silica. Ijolite-urtites are by and large composed of nepheline and aegirine-augite, which is why they have a gray-green color. Minerals from the category of non-ferrous minerals of this complex are pyroxene and apatite.

Almost in the middle of the mountains there is a complex of medium-grained nepheline syenites. The composition of these rocks includes: feldspar, nepheline, aegirine and alkaline amphibole. In the center of the mountain there is a foyaite complex, it stretches over almost one third of the mountain range. The mineral composition is potassium-sodium feldspar and nepheline, and non-ferrous minerals are alkaline amphibole, aegirine, biotite, sphene, apatite and others.

Academician Alexander Fersman believed that the Khibiny tundra is a natural mineralogical gallery. And of course, the way it is, one hundred and eight varieties of minerals are mined in the mountain range, more than ten of which are of great value. These are apatites, sphene, aegirine, nepheline, titanomagietite, lovchorrite and others. At the same time, the remains of mining, which are commonly called "nepheline tailings", are the main deposit, it is thanks to them that the needs of the territory in the required materials will be provided for decades.

Gypsum has not lost its popularity even today, although it has been known since antiquity. Many modern materials to this day cannot compete with him. It is used in the ceramic, porcelain and faience, oil industry, construction and medicine. Gypsum is in demand in sculpting sculptures, and is divided into different grades depending on the strength obtained.

Definition

Gypsum has a grayish or white color. The grinding of the material is fine, it is obtained from natural gypsum after processing, it is fired at a temperature of up to 190 ˚С. The substance quickly seizes, is a fast-hardening binder. It is used for plastering, in the manufacture of gypsum construction items, gypsum concrete, castings, and also as an additive to binders such as cement and lime.

The material is calcined in rotary kilns, after which the raw material is ground to form a powder. To date, two varieties of gypsum are known - fibrous and granular. The first is called selenite, the second - alabaster.

Specifications

If you want to use plaster, the grades and their characteristics should be of interest to you. There are 12 of them in total. All of them have very similar characteristics. Among the main features of building gypsum, density should be distinguished, which varies from 2.60 to 2.76 g / cm 2. The material has a dense fine-grained structure. In loose-fill form, the density varies from 850 to 1150 kg/m 2 .

If the material is presented in a compacted form, then this parameter varies from 1245 to 1455 kg / m 2. A rather important feature is the drying time. Among the main advantages, fast hardening and setting should be highlighted. At the 4th minute after kneading, the gypsum begins to harden, after 30 minutes it solidifies completely. Ready solution in connection with this must be consumed immediately.

On melting point and bulk density

To slow down the setting, water-soluble is added to the gypsum. It is important to mention also the specific gravity, which is the ratio of mass to the volume it occupies. Volumetric and bulk weight are approximately the same. Quite often, consumers are also interested in what temperature gypsum undergoes. This characteristic is also called the melting point. Heating can occur up to 700 ˚С without destruction. Fire resistance is quite high. Destruction occurs only 8 hours after exposure to high temperature.

If you want to purchase the described material, then you should be interested in gypsum grades for strength. For example, a building material in compression has a strength parameter of 4 to 6 MPa. If you have high-strength gypsum in front of you, then this parameter varies from 15 to 40 MPa. Dried specimens can be up to three times stronger. The material also complies with state standards 125-79 (ST SEV 826-77).

Thermal conductivity and solubility

Among the characteristics it is necessary to highlight the ability to conduct heat. Gypsum does not do well with this. Thermal conductivity is 0.259 kcal/m deg/h, which is true for temperatures from 15 to 45 ˚С. Solubility in one liter reaches 2.256 g. These figures are correct at 0 ˚С. If the temperature is increased to 15°C, the solubility is 2.534 g. At 35°C, the solubility increases to 2.684 g. If heating is continued, the solubility decreases.

additional characteristics

When studying the brands of gypsum for artificial stone, you may note that it is not always convenient that the material sets so quickly. When working with solutions, you must take into account that the hardening dough seizes and rejuvenates when mixed. But if such a solution is applied to the surface, it will no longer have the necessary strength, and when it dries, the material will begin to collapse, become covered with cracks. Therefore, gypsum-based mortars should be prepared in small quantities that you can use within a few minutes.

In order to reduce the adhesion, clay or lime mortar should be added. For the same purpose, a special moderator from a solution of borax is used. All these mixtures are prepared in water. Hardened gypsum is characterized by high strength and low density, which varies in the range of 1200-1500 kg / m 3, such a material is almost two times lighter than cement. This suggests that the composition is less thermally conductive.

Stamps

There are 12 grades of gypsum, as mentioned above. They include some varieties of gypsum, among them should be highlighted:

• building;
• technical; modified;
• molding.

The first is marked as G4 or G5 and is used for plastering and the manufacture of various building elements. The technical variety is marked G5 and is a molding model material. When considering gypsum grades, you should pay attention to the modified variety, which is labeled as G16 and is used for sealing joints, grouting primers and putties.

Molding plaster is marked as follows: G10, G18. It is used in the ceramic, aviation and automotive industries. Among the main areas of application, it is worth highlighting the manufacture of molds for casting alloys and non-ferrous metals. Molding plaster has found its wide distribution in the manufacture of models for sculptural work.

If you are interested in building gypsum brands, you should pay attention to the markings from G-2 to G-7. These materials belong to group B, and their compressive strength varies from 0.2 to 0.7 MPa, which is a limit of 2 to 7 kgf/cm 2 . In this case, the onset of setting occurs at the sixth minute. The setting ends no later than half an hour. The brand of building gypsum is called alabaster. This is the only binder that expands and increases in volume up to 1% during the hardening process, but cement and lime paste shrink.

More about brands: construction

The construction grade of gypsum is used for the manufacture of parts, plastering and the formation of partition slabs. Work with such a solution must be carried out in a short time - from 8 to 25 minutes. The final value will depend on the specific brand. At the beginning of hardening, the material gains approximately 40% of the final strength.

Due to the fact that during hardening cracks do not form when the solution is mixed with a lime composition, which is necessary to obtain plasticity, it is possible not to use different aggregates. In this case, the setting time will be reduced due to hardening retarders.

High strength polymer grades

In terms of composition, the high-strength grade is similar to the construction grade, however, the latter has smaller crystals, while the high-strength grade has large fractions, therefore it has less porosity and high strength. Such gypsum is made by means of heat treatment in equipment under tightness conditions, where a gypsum stone is placed.

Considering the definition of the brand of gypsum, you can understand that the scope of its use is quite extensive. Building mixtures are made from raw materials and fireproof partitions are formed. Gypsum is used to make various forms for porcelain and faience sanitary ware. A high-strength variety is used in dentistry and traumatology. But orthopedic traumatologists are more familiar with synthetic polymer gypsum, on the basis of which gypsum bandages are made for dressings for fractures. Among the main advantages of the polymer brand should be highlighted:

• "easy overlay";
• moisture resistance;
• ease;
• the ability to control bone fusion.

The material allows the skin to breathe, because it has good permeability.

Brand Definition

If you are interested in how to determine the brand of gypsum, then you should know that marking is carried out according to some indicators, among them should be highlighted:

• strength;
• fineness of grinding; gripping speed.

The grade can be determined by a bending and compression test of standard samples. They have the following dimensions: 4 x 4 x 16 cm. Tests are carried out 2 hours after molding. First, the flexural strength is determined, then the compressive strength. During this time, crystallization and hydration are completed.

According to GOST 129-79, 12 grades of material for strength are established. The number after the letter indicates the lower compressive strength. For a gypsum binder, the start and end of setting is an important factor. According to these parameters, the material is divided into three groups - A, B, C. According to the fineness of grinding, which is determined by the rest of the sample during sieving, the binder is divided into three groups: coarse, medium, fine. Density can be true and bulk. The 1st varies from 2650 - 2750 kg / m 3, the 2nd - from 800 - 1100 kg / m 3.

Characteristics of gypsum G5

This brand of building gypsum has a compressive strength of 5. In bending, this parameter is 2.5. With the help of this composition, it is possible to repair surfaces, close up cracks, depressions, potholes and mount electrical installation products. Gypsum allows you to fix beacons and profiles during plastering.

Another area of ​​​​use of such gypsum is the manufacture of dry building mixtures for facing works. The degree of grinding is 14% when sieved through a sieve with cells with a size of 0.2 mm. The compressive strength of the samples is 5 MPa. Setting times vary from 6 to 30 minutes. Considering the characteristics of gypsum grade G 5, you should pay attention to the flexural strength, which is 25 kg / cm 2.

Characteristics of gypsum G10

This gypsum is a high-strength, finely ground white powder. In its pure form, it is transparent and colorless, and in the presence of impurities it has a yellowish, gray, brown or pink tint. Gypsum brand G 10 is a fire-resistant non-combustible material that does not have toxic components. Its acidity is similar to that of human skin.

The compressive strength is 100 kgf/cm 2 . The normal hardening variety begins to polymerize in the sixth minute, the end of curing is reached in the 9th minute. The material can be used in sculptural work, in the ceramic industry, in the aviation and automotive sectors, as well as for high-quality finishing work. This gypsum is also used in the production of decorative stone.

Finally

Gypsum has been known to man for a long time, but today more and more extensive areas of use are found for it. It is used not only in industry, but also for private purposes. It becomes part of fireproof partitions and products for various purposes.

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Each of us is familiar with culinary failures - sticky pasta, meat that most of all resembles a piece of old rubber, unbaked pies and a million more “masterpieces” that make you disappointed in your own abilities.

website I have collected for you some typical mistakes of novice cooks, getting rid of which you will turn into a culinary guru. At least they should.

Rinse the pasta

Rinsing the pasta with cold water after cooking can make any Italian faint - after all, valuable starch remains on its surface, which helps the sauce to be better absorbed. Moreover, Italian housewives use the water in which pasta was cooked to dilute sauces that are too thick.

Cooking tomatoes along with other vegetables

One of the most common mistakes novice cooks make is putting tomatoes in a dish along with potatoes, carrots, and other vegetables. The acid in tomatoes slows down the cooking process of other vegetables, which can take longer to cook. For the same reason, vinegar is added to dishes when the dish is almost ready to be served.

Salt the broth at the beginning of cooking

Everything is very simple here - if you salt the broth at the very beginning of cooking, then there is a risk of getting a very salty dish, since the water will boil away during cooking. By the way, the secret to a delicious broth is to put the meat in cold water. But if you plan to cook excellent meat, then the water intended for cooking it should boil.

Use a blender for mashed potatoes

A blender, of course, is a great helper in preparing a lot of dishes, but not when it comes to mashed potatoes. The most delicious “crushed” is obtained if you make it the old fashioned way, with the help of a pusher, and then beat with an ordinary fork. By the way, professional chefs carefully drain all the water in which the potatoes were boiled, and even dry them right in the pan.

Use too little or too much spices

Chefs have a joke that an undersalted dish is much worse than an oversalted one. The same applies to any seasonings and spices - their lack can affect the quality of the dish, literally depriving it of taste. But it’s not worth putting all the spices that just show up on the shelves - “over” in this case is just as bad as “under”.

Putting a lot of toppings on pizza

At first glance, it may seem that the more toppings in the pizza, the more beautiful and tastier it turns out. However, this is not the case - when preparing pizza, it is better to strictly adhere to the amount of ingredients indicated in the recipe. So you can get a crispy dough that will not sag and will give you the opportunity to eat pizza with your hands - just like they do in her homeland.

Boil dough products in a small amount of water

Pasta, dumplings, dumplings and other dough products must be boiled in plenty of water. If there is not enough water, then the dough risks turning into a paste, and then instead of an appetizing dish, you will get something that least of all resembles delicious food. In addition, pasta or dumplings will stick not only to each other, but also to the walls of the pan, and washing it, you see, is still a pleasure.

Shred the onion ahead of time

Finely chopped onion becomes bitter very quickly, so dishes with it also begin to taste bitter. The same thing can happen if you cut an onion with a dull knife. Therefore, you need to chop the onion right before laying it in the dish and only with a sharp knife.

Cut steak meat along the grain

Even the best meat can be successfully turned into a real "shoe sole" if cut along the grain. When frying, such pieces will shrink and become very tough. To avoid this, the meat must be cut across the fibers - then it will not change its shape during cooking and remain soft.

Extinguish soda with vinegar

Despite the fact that our grandmothers used this technique, there is no practical sense in it. When quenching, all the carbon dioxide, which was supposed to give the dough airiness, goes into the air, but the soda, which remained outstanding during this chemical experiment, is responsible for raising the dough. In one of the old recipes, to give the dough airiness, it is recommended to use this technique: dissolve a spoonful of soda in 1/4 cup of water, and a teaspoon of citric acid in another glass with the same amount of water, and then add to the dough.

Bake potatoes immediately after slicing

Agree, baked potato wedges with a crispy crust look very appetizing. On the picture. In practice, it is very difficult to achieve such a crust. However, if you soak the slices for a couple of hours in cold water before putting them on a baking sheet, then the excess starch will go away, and after baking, the potatoes will look exactly like on the pages of culinary magazines.

Boil vegetables for a long time

Even if you are not a fan of al dente dishes, it is worth remembering that all green vegetables, such as broccoli or spinach, do not tolerate long cooking. Therefore, for their preparation, such a culinary technique as blanching is used - a short-term heat treatment in boiling water. The duration varies from 2 to 5 minutes and depends on the selected vegetables. This method of cooking will not only preserve their taste and color, but also minimize the loss of vitamins.

Saute onions and carrots at the same time

One of the most common mistakes when creating a soup sauté (mistakenly called a "sauté") is putting onions and carrots in the pan at the same time. In fact, first of all you need to put the onion, wait until it starts to become transparent, and only then add the carrots. The secret is simple: contrary to popular belief, the onion takes longer to cook, and when it burns, it acquires a bitter taste, which is transferred to the dish.

Skip sugar when preparing savory meals

This, of course, is not about adding sugar to the soup in the proportions used to make jam. However, a small pinch of sugar in borscht, hodgepodge, goulash, or other dishes - especially those containing sour ingredients like tomatoes - can improve the taste qualitatively. By the way, this rule also works in the opposite direction - a pinch of salt in sweet dough dishes gives baked goods a richer taste.

The average household size varies by country from 2 to 8 people

The most important characteristic of a household is, first of all, its average size, calculated as the ratio of the number of all household members to the number of households.

According to the data provided by the UN, the average size of a household varies by country from 2 to 8 people. About 18% of the world's population (according to UN estimates for mid-2017) lives in countries where the average household size does not exceed 3 people, 50% - in countries where it does not reach 4 people (Fig. 1). Just over 10% of the world's population lives in countries where the average household size is 5 people or more. In countries where the average household size is 6 or more, only 6% of the world's population lives, 7 or more - 2.5%.

The median value of the average household size among the countries for which it is available is 3.8, in the central half of the countries (excluding the 25% of the countries with the smallest and 25% of the countries with the largest value of the indicator) it varies from 2.8 to 4.8.

Estimates of average household size are not available for 34 of the 233 states and entities covered by population statistics. About 1% of the population lives in these countries. Of the largest among them in terms of population, we note Angola, Syria, the United Arab Emirates, Eritrea and Turkmenistan.

Figure 1. Average household size (person) and share of world population cumulatively in ascending order of average household size (%)* by country

* world population as of mid-2017 according to the average variant of the UN forecast

Source: United Nations, Department of Economic and Social Affairs, Population Division (2017). Household Size and Composition Around the World 2017 – Data Booklet: 12-29; World Population Prospects: The 2017 Revision, DVD Edition. POP/DB/WPP/Rev.2017/POP/F01-1.

Small households - on average less than three people per household - are common in Europe and North America, large households - five or more people - in Africa and the Middle East.

Among the 50 African countries for which the UN database has average household size, it ranges from 3.2 in South Africa to 8.3 in Senegal, with a median of 4.7 (Figure 2). Only 6 African countries have an average household of less than 4 people (in addition to South Africa, Lesotho, Ghana, Botswana, Kenya and the Seychelles). However, there are also few countries where, on average, more than 6 people live in a household - only 4 in addition to Senegal (Gambia - 8.2, Guinea - 7.2, Niger - 7.1, Mauritania - 6.1).

Among the 47 Asian countries for which the UN database has average household size, it ranges from 2.4 in Japan to 8.0 in Afghanistan and Oman, with a median of 4.4. Less than 3 people is the average household size not only in Japan, but also in South Korea (2.5), Cyprus (2.8) and Hong Kong Special Autonomous Region (SAR) of China (2.9). In China and Macau (also the SAR of China), as well as in Israel, it is 3.1, and in 11 other Asian countries from 3.3 to 3.9. In addition to Afghanistan and Oman, Iraq (7.7), Pakistan (6.8), Yemen (6.7) and Tajikistan (6.3) have a large average household size. In other countries of the region, it does not reach 6 people.

Among the 43 countries in Europe, the average household size ranges from 1.9 in Monaco to 3.9 in Albania, with a median of 2.4. In addition to Monaco, Denmark, Finland and Germany have the smallest average household sizes (2.1). Only in the 4 European countries for which estimates are presented do households average more than 3 people. Apart from Albania, Macedonia (3.6), Montenegro (3.2) and Bosnia and Herzegovina (3.1).

Among 39 countries in Latin America (hereinafter including the Caribbean), the average household size ranges from 2 in Montserrat to 5.2 in Nicaragua. The median value is 3.3. Twelve countries in the region have an average household size of less than 3 people, including Uruguay, Puerto Rico and Dominica. On the other hand, only in 6 countries it exceeds 4 people - in addition to Nicaragua, in Guatemala (4.8), Paraguay (4.6), Haiti (4.4), El Salvador and Belize (4.1 each).

In all North American countries represented in the UN database, the average size is less than 3 people: in the USA - 2.6, in Canada and Bermuda - 2.3.

Among the 17 countries in Oceania for which average household size estimates are provided, it ranges from 2.5 in Australia to 6.9 in the Marshall Islands. In addition to Australia, New Zealand has a small household size (2.7). The island states of Melanesia, Micronesia and Polynesia are characterized mainly by relatively large households (5 people or more).

Figure 2.Average household size by countries of large regions of the world, people

Source: United Nations, Department of Economic and Social Affairs, Population Division (2017). Household Size and Composition Around the World 2017 - Data Booklet: 12-29.

Data from different years show that in recent decades, the average size of a frequent household has been gradually decreasing in almost all countries of the world. Thus, in France it decreased from 3.1 in 1968 to 2.3 in 2011, in Kenya - from 5.3 in 1969 to 4 people in 2014. The most important factor in reducing the size of the household was a decrease in the birth rate, an increase in life expectancy (including healthy, without restrictions in everyday life), changes in marriage patterns, increased migration mobility, changes in education, employment and the housing market.

A converging lens with a focal length f = 30 cm gives a clear enlarged image on the screen if the following condition is met: , where

d 1 - distance from the object to the lens (cm);

d 2 - distance from the screen to the lens (cm);

f - focal length (cm).

The distance between the screen and the lens d 2 can vary from 90 to 120 cm.

Find the minimum distance from the object to the lens so that its image on the screen remains clear. Give your answer in centimeters.

Solution

Let's express d 1 from the ratio, under which the enlarged image will be clear:

\frac(1)(d_(1)) + \frac(1)(d_(2)) = \frac(1)(f)

\frac(1)(d_(1)) = \frac(1)(f) - \frac(1)(d_(2))

We reduce the right side to a common denominator and express d 1:

\frac(1)(d_(1)) = \frac(d_(2)-f)(f\cdot d_(2))

d_(1) = \frac(f\cdot d_(2))(d_(2)-f)

Let's determine what distance d 1 will be at the boundary values ​​​​d 2 (d 2 \u003d 90 cm and d 2 \u003d 120 cm) and find the smallest among them. Focal length of the lens f = 30 cm.

For d 2 = 120 cm we get:

d_(1) = \frac(30 \cdot 120)(120-30) = \frac(30 \cdot 120)(90) = 40 cm

For d 2 = 90 cm:

d_(1) = \frac(30 \cdot 90)(90-30) = \frac(30 \cdot 90)(60) = 45 cm

The smallest of them is 40 cm.