Hydroxides and Basic Carbonates

The mechanisms by which such fillers reduce polymer flammability is discussed in depth in Chapter 6. In this chapteg only the production of the fillers, and the properties relevant to their use as fillers and flame retardants are discussed. 

This is by far the most widely used flame-retardant filler, being available at relatively modest cost and with a wide range of particle sizes, shapes and surface treatments to suit various applications. Although its chemical structure is that of the hydroxide, it is often referred to as alumina trihydrate (AI2O3.3H2O) or simply ATH. There is more than one crystal form of aluminium hydroxide, but that used as a flame retardant is gibbsite. For convenience the common acronym, ATH, will be used throughout this book. 

ATH is a white, non-toxic, material, which is soluble in strong acids and alkalies. It has a specific gravity of 2.4, is relatively soft (Mohs hardness about 3) and nonabrasive. It starts to decompose at about 200 °C with the loss of 34.6% by weight of water when fully decomposed. 

The Bayer process results in a waste stream known as red mud , which contains considerable amounts of sodium aluminium silicates. These can be converted into ATH if the red mud is mixed with limestone and sodium carbonate and calcined, to form sodium aluminate. This is extracted into water and gibbsite then precipitated as in the Bayer process. These products are known as sinter hydrates. They are whiter than the Bayer products as the calcination destroys the organics, but they still contain similar levels of sodium. 

The main problem of the Bayer and sinter processes from a filler point of view, is the relatively large size of the product. Although this can be ground to produce finer grades, there is an economic limit to this. Also the grinding tends to produce platy particles, due to preferential cleavage of the ATH along certain crystal planes. 

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Structural changes of alkaline earth and alkali ions promoted alkaline earth oxides as well as other catalytic systems after eatalytic reaction have been studied by XRD, IR, DTA and other analytical techniques (Table 1 ). The formation of hydroxides and basic carbonates has been identified in XRD patterns for the catalyst samples consisting of either CaO or MgO. IR spectroscopic studies also support the formation of hydroxides layer after catalytic reaction. Activities and selectivities of different samples were shown in Table- 2. 

Coprecipitation of ferric chloride in excess NaOH and in the presence of barium carbonate forms a mixture of mixed hydroxides and basic carbonates which, upon calcination at 710°C, form the barium ferrite. The magnetic properties are optimized by subsequent heat treament at 950 °C. This method produces plateletshaped particles with an average size of 0.3 pm [110]. Another technique involves oxidation of feirous oxalate by hydrogen peroxide in the presence of excess oxalic acid. The addition of barium carbonate (Ba/Fe = 1/12) forms.mixed complexes of... 

The loaded organic phase is stripped of beryUium using an aqueous ammonium carbonate [506-87-6] solution, apparently as a highly soluble ammonium beryUium carbonate [65997-36-6] complex, (NH 4Be(C02)3. AU of the iron [7439-89-6] contained in the leach solution is coextracted with the beryUium. Heating the strip solution to about 70°C separates the iron and a smaU amount of coextracted aluminum as hydroxide or basic carbonate... 

Hydroxides and basic salts. The necessity for careful control of the pH has long been recognised. This is accomplished by making use of the hydrolysis of urea, which decomposes into ammonia and carbon dioxide as follows ... 

Recently, the influence of the preparation method of various MgO samples on their catalytic activity in the MPV reaction of cyclohexanone with 2-propanol has been reported 202). The oxides were prepared by various synthetic procedures including calcination of commercially available magnesium hydroxide and magnesium carbonate calcination of magnesium hydroxides obtained from magnesium nitrate and magnesium sulfate sol-gel synthesis and precipitation by decomposition of urea. It was concluded that the efficiency of the catalytic hydrogen transfer process was directly related to the number of basic sites in the solid. Thus, the MgO (MgO-2 sample in Table IV) prepared by hydration and subsequent calcination of a MgO sample that had been obtained from commercially available Mg(OH)2 was the most basic and the most active for the MPV process, and the MgO samples with similar populations of basic sites exhibited similar activities (Table IV). 

An industrial process [5.289] operates with solutions of zinc sulfate and zinc chloride in the ratio 1 2. Basic zinc carbonate is precipitated by feeding simultaneously the zinc salt solution and a mixed solution of sodium hydroxide and sodium carbonate into a reactor charged with water. The precipitated product is intensively washed several times and then spraydried. 

After the books are removed from the processing chamber, during the overnight recovery, or subsequently in the library, the magnesium hydroxide and magnesium carbonate can release moisture or carbon dioxide to the ambient air to form the basic magnesium carbonate [MgO MgC03 Mg(0H2)] and function as the alkaline reserve. 

Hydroxides, hydroxy carbonates, and hydrates of aluminum, calcium, and magnesium that potentially meet these requirements are shown in Table 7.1, together with relevant thermal properties and gaseous products evolved on decomposition. However, of those in commercial use, aluminum hydroxide makes up about 90% of the market by tonnage, with magnesium hydroxide and basic magnesium carbonate products being used in niche applications. 

Addition of ammonium carbonate to a solution containing an actinide(III), (IV),(V) or (VI) ion gives the following results. Only actinide(VI) ions form soluble carbonato complex ions. Actinide(III) and (IV) ions precipitate as their hydroxides or basic carbonates, and actinide(V) ion precipitates as a double carbonate. Therefore, in dilute ammonium carbonate medium, U(VI) ion can be separated primarily from Np(V), Pu(IV), Am(III) and Cm(III) ions. Further addition of ammonium carbonate leads to complex ion formation and the dissolution of actinide(IV) precipitates. However, most of the actinide(III) and (V) ions remain as precipitates under this condition. Crystalline precipitates of actinide(IV) and (VI) carbonato complex anions are formed by addition of hexamminecobalt(III), hexaureachromium(III) or hexa-mminechromium(III) salt to the ammonium carbonate solution containing actinide(IV) and (VI) ions. 

The temperature required for the reduction of cobalt oxides to the metal appears to be somewhat higher than for the reduction of nickel oxide. The catalyst with a higher catalytic activity is obtained by reduction of cobalt hydroxide (or basic carbonate) than by reduction of the cobalt oxide obtained by calcination of cobalt nitrate, as compared in the decomposition of formic acid.91 Winans obtained good results by using a technical cobalt oxide activated by freshly calcined powdered calcium oxide in the hydrogenation of aniline at 280°C and an initial hydrogen pressure of 10 MPa (Section... 

The application of mechanical activation for the synthesis of the mentioned above compounds started with the activation of the mixtures of anhydrous oxides [15]. Then, barium oxide (or carbonate) in the mixture was replaced with barium nitrate [16], while copper oxide was replaced with copper hydroxide or basic carbonate Cu2C03(0H)2 [17]. Later, yttrium and copper nitrates were used instead of oxides, while barium hydroxide Ba(OH)2 or Ba02 were used as barium-containing compound [18] finally, the mixture of oxides was activated in the presence of water added for the purpose of obtaining well-molding pastes [19]. After activation, the mixtures were annealed at increased temperature, but the synthesis... 

Special considerations magnesium hydroxide and basic magnesium carbonate are used as flame and smoke retarding additives ... 

The hydroxides are precipitated in a gelatinous mass by the action of the alkalies upon the hot solutions. If the alkaline solution is added to a rare earth in the cold, the precipitate is usually a basic salt or a mixture of the-hydroxide and basic salt. The hydroxides are not soluble in excess of reagent, but dissolve readily in acids and generally absorb carbon dioxide from the air. 

A small fraction of the zinc initially exists in the aquatic phase as soluble inorganic zinc compounds. Zinc chloride and zinc sulfate are very soluble in water but hydrolyze in solution to form a zinc hydroxide precipitate. Hydrolysis may lower pH, but the buffering action present in most natural water prevents a significant alteration in pH. The precipitation of zinc hydroxide and zinc carbonate was studied by Patterson et al. (1977), who found that zinc hydroxide precipitates faster than zinc carbonate. Zinc carbonate is soluble in pure water at 25°C at concentrations of 107 mg zinc/L. The hydroxide is soluble only at concentrations of <0.2 mg zinc/L. As a result, some of the inorganic forms of zinc that are expected to be present in water are basic carbonate (Zn 2[OH]2CO), hydroxide (Zn[OH]2), and silicate (Zn2SiO) (Florence 1980 NAS 1977). When the pH is 8, most of these compounds will precipitate however, as the pH decreases, more and more of these compounds will dissolve and remain in the water phase (Callahan et al. 1979). 

Zinc is precipitated from purified zinc salt solutions as hydroxide, or basic carbonate, which is washed, filtered and dried. The resulting compound is subsequently calcined. By varying the precipitation and calcination conditions, different grades of ZnOs are prepared. At low calcination temperatures transparent ZnO, which is actually the basic carbonate, is obtained. ZnOs produced by wet chemical methods are particularly pure, since very pure zinc salt solutions can be obtained. 

Sulfur oxides and other corrosive species are brought to react with the zinc surface in two ways dry deposition and wet deposition. Sulfur dioxide has been observed to deposit on a dry surface of galvanized steel panels until a monolayer of SO2 formed (Maato, 1982). In either case, the sulfur dioxide that deposits on the surface of the zinc forms sulfurous or other strong acids, which react with the film of zinc oxide, hydroxide, or basic carbonate to form zinc sulfate. The conversion of sulfur dioxide to sulfur-based acids may be catalyzed by nitrogen compounds in the air—usually referred to collectively as NQt compounds—and it is believed that this factor may affect corrosion rates in practice. The acids partially destroy the Film of corrosion products, which will then re-form from the underlying metal, so causing continuous corrosion by an amount equivalent to the film dissolved, hence to the amount of sulfur dioxide absorbed. Above about 85% RH, corrosion rates increase further—probably as a result of the formation of basic zinc sulfates. 

In natural atmospheres, once the moisture layer has been established, zinc hydroxide rapidly forms on this film, in this case due to an electrochemical mechanism. The formation of a moisture layer of sufficient thickness, together with the action of atmospheric CO2, leads to the formation of basic zinc carbonates from the initially formed hydroxide [3, 5]. Both the hydroxide and the carbonates are very stable and have a protective character, and they therefore tend to inhibit zinc corrosion in atmospheres without contamination. However, if the... 

Often, the compound to be oxidized is made a ligand, and the oxidation can then be intramolecular, as in the Dow phenol process [Eq. (53)], where the benzoate of basic copper(II) benzoate is oxidized to salicylate by hydroxide and then carbon dioxide is eliminated to yield phenol. 

The effectiveness of intumescent flame retardants is frequently reduced when fillers are added. Interactions can be either chemical or physical. Materials which are basic in character such as aluminium and magnesium hydroxides and calcium carbonate tend to interfere chemically with the phosphoric acid precursor in the intumescent system, presumably forming inorganic phosphates. Such antagonistic behaviour can be easily recognized by an almost complete lack of char formation. 

Similar observations of PDMS-hydrophobed silica antifoam deactivation on inorganic carrier materials have been reported in a pharmaceutical context. The antifoam performance of antiflatulent preparations with PDMS-hydrophobed silica mixed with basic antacid carriers, such as aluminum hydroxide and magnesium carbonate, has been shown to deactivate after the ingredients were either granulated or compressed into tablets [81, 82]. Analysis of the molecular weight distribution of... 

The chemical precipitation method that is used most is precipitation of metals as hydroxides and basic salts with lime. Sodium carbonate can be used to precipitate metal hydroxides (Fe(0H)3 xH20) carbonates (CdCOs), or basic carbonate salts (2PbC03 Pb(0H)2). The carbonate anion produces hydroxide by virtue of its hydrolysis reaction with water ... 

The use of plasticizers that are themselves flame retardants is discussed in Chapter 9, as well as formulating so as to optimize their effect and to minimize their tendency to be less efficient than flammable plasticizers. Chapter 9 also considers combustion mechanisms. A useful review of the latter has been given by Green. This chapter presents the use of inorganic additives as flame retardants and smoke suppressants as a basis for formulation for specific applications. These additives can be divided into antimony compounds and derivatives the class of metal hydroxides, carbonates, and basic carbonates and a further range of molybdenum, zinc, and iron compounds. 

The third group of active components is obviously the reactive atmospheric gases. AU nonaqueous solutions contain unavoidable traces of O2, N2, H2O, and CO2. AU of these gases are reactive with lithium and Uthiated carbon. Their surface reactions form Li oxides, Li nitrides, Li hydroxide, and Li carbonate, respectively [42]. We should add to this list of contaminants the decomposition products of LiPFe- This salt decomposes to LiF and PFj (an equilibrium reaction) [43]. The latter compound readily hydrolyzes to form HF and PFsO. Hence, LiPFg solutions always contain HF. HF reacts with both electrodes and basic surface species to form surface UF as a major solid product. 

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