Why is pbcl2 solid

The dashed line shows the observed sintered front. Figure 4. Figure 5. Figure 6. The image shows how the Pb species are enriched on the furnace-facing side of the salt particles and even penetrate into the original salt particles, resulting in K depleted areas.

The table also shows the observed Pb-containing species, on and within the oxide layer, with different deposit materials. Figure 7. Figure 8. Figure 9. Figure Niemi and D. Lindberg is greatly appreciated. More by Jonne Niemi. Box , FI Tampere, Finland. More by Hanna Kinnunen. More by Daniel Lindberg.

More by Sonja Enestam. Cite this: Energy Fuels , 32 , 8 , — Article Views Altmetric -. Citations 9. Combustion of recovered waste wood or recycled wood is known to cause severe corrosion problems on furnace walls. Several studies have focused on fireside corrosion in waste-fired boilers. The first one was observed in laboratory testing and the latter one has been found from boiler heat transfer surfaces.

The novel testing method has been used earlier for alkali chloride-alkali sulfate mixtures, increasing the understanding of alkali chloride migration within boiler tube deposits and clarifying the importance of understanding the effects of temperature gradients on corrosion reactions.

Waste wood is composed of different types of wood fractions and can also include high amounts of Zn. Based on laboratory studies, ZnCl 2 has been proven to be corrosive at similar temperatures as PbCl 2. Despite the fact that S is a good corrosion prevention agent against alkali chloride induced corrosion, its effectiveness against PbCl 2 induced corrosion is still not fully understood.

Folkeson et al. They reported a positive effect with stainless steel but low alloyed steel corroded regardless of the S feed. In addition, laboratory measurements have shown K 2 SO 4 to react with PbCl 2 and to form a caracolite-type mixture, K 3 Pb 2 SO 4 3 Cl, which also induces increased corrosion with carbon steel material.

The purpose of this study is to investigate the interaction of gaseous PbCl 2 with K and Na salts that are found in boiler deposits, with special focus on the formation of corrosive alkali lead compounds. The laboratory tests were performed using two different synthetic deposit materials that were applied on an air-cooled probe on adjacent alloy samples separated by a heat-resistant barrier. Although in a boiler environment, other ash forming elements are also likely to affects the behavior of PbCl 2 , this paper concentrates on a simplified system in order to gain a better understanding of the detailed phenomena.

The focus was set to study the vaporization, condensation, and reactivity of PbCl 2 within the other deposit. Experimental Section. The principal experimental equipment was the same as used by Lindberg et al.

The probe is inserted into a tube furnace where it is heated up. The difference in the probe and furnace temperature leads to a steep temperature gradient over the deposit material, simulating a temperature profile of a boiler deposit.

Deposit thickness of approximately 10 mm was used throughout. At the end of the experiments, the probe is removed from of the furnace and rapidly cooled down to room temperature.

High Resolution Image. After cooling, the deposit material is glued to the sample ring with a few drops of epoxy resin. Differing from the experiments of Lindberg et al. The ring no. The deposit materials were separated by a wall formed out of fire-sealant paste consisting of sodium silicates and kaolin. The same size fraction was also used for the other alkali salts. As the temperature profiles are expected to be similar between samples with the same temperatures but with different target deposit materials, also similar vaporization and diffusion behavior for the PbCl 2 was expected to occur in experiments with different target deposit materials.

The condensation of PbCl 2 in the target deposit might differ between different compositions due to reactions and interactions e. The experimental matrix is summarized in Table 1. Table 1. Experimental Matrix. Table 2. Results and Discussion.

The experiments with SiO 2 were conducted in order to study the gas-phase migration of PbCl 2 to, and within, a chemically inert deposit.

SiO 2 was chosen as the deposit material because it does not react or form melt with PbCl 2. The inertness offered a way to focus only on the migration of PbCl 2 without considering the reactions or interactions with the deposit material.

In addition, no significant corrosion of the steel was observed. In addition, significant corrosion was observed already after 4 h exposure. Pure PbCl 2 was observed within the oxide layer but not in the deposit layer itself. Although the deposit layer did not contain PbCl 2 , it is likely the PbCl 2 migrated to the oxide layer via gas-phase.

The lack of continuous PbCl 2 feed results in a case where the PbCl 2 that had already migrated into the SiO 2 deposit would revaporize into the gas-phase once the partial pressure of PbCl 2 in the furnace air drops. The experiments with NaCl showed that PbCl 2 migrates to, and within, the deposit via gas-phase. The solidus temperature corresponds well with the fact that PbCl 2 inclusions in the NaCl particles were observed also in particles just above the steel surface, i.

However, the amount of PbCl 2 was observed to be lower and the oxide layer was thinner. This can be explained by the eutectic melting of the NaCl—PbCl 2 system. In a case where there is a surplus of NaCl when compared to PbCl 2 , all of the PbCl 2 will be included in the liquid-phase, lowering its partial pressure in the gas-phase and inhibiting the gas-phase migration to the steel.

However, signs of melting were observed throughout the deposit, indicating a presence of PbCl 2 during the experiment. In addition, the oxide layer was observed to be rich in PbCl 2. The Pb species were found within a certain distance from the steel and also in an enriched area see Figure 3. NaCl was also observed within the deposit, supporting the proposed overall reaction. The formation of NaCl within the deposit further affects the melting behavior of the deposit.

Approximately in the middle of the deposit, a threshold between a sintered and nonsintered layer was observed, indicating the location of melt within the deposit Figure 3. The NaCl was observed exclusively on the furnace-facing side of particles, indicating gas-phase migration toward the steel surface via vaporization-condensation of NaCl, 19,20 or that the furnace-facing side was the reaction site. Signs of melting were observed at constant distance from the steel surface, roughly in the middle of the deposit.

The uppermost particles of the deposit had not sintered, but closer to the steel clear signs of sintering were observed. This implies that sufficiently low local temperature was needed for the condensation of the PbCl 2. The majority of the Pb-containing species observed in the deposit were found just above the region where the sintering started, in the form of K 2 PbCl 4.

The Pb-containing species found within the deposit layer were either observed on the furnace-facing side of particles or entrapped within a KCl particle or matrix. The presence of Pb-species on the furnace-facing side of KCl particles implies gas-phase migration to be responsible for the Pb presence in the deposit.

The mechanism is similar as described by others. The higher temperature at the PbCl 2 source deposit results in higher concentration of PbCl 2 in the gas-phase, which increases the condensation of PbCl 2 at the target deposit. The entrapped Pb-species in and between KCl particles indicate that melting has occurred. The formation of K 2 PbCl 4 can explain the difference. The need for reactions to form components that are able to vaporize could function as a limiting step for the revaporization back to the furnace.

In addition, there were signs of sintering at the outer edge of the deposit. In addition, the whole deposit displayed a sintered structure. Close to the steel surface, there was a compact region Figure 5 that was enriched in Pb and Cl. Pb and Cl were also observed both above and below the compact region, mainly on the furnace-facing side of the particles.

Similar behavior was reported by Kinnunen et al. The layers above the compact region had a composition corresponding approximately to K 3 Pb 2 SO 4 3 Cl, which was first observed by Kinnunen et al. The K 2 SO 4 particles above the compact region had clearly experienced a presence of a molten phase during the experiment.

In addition, minor amounts of KCl were found within the deposit, which supports the formation of K 3 Pb 2 SO 4 3 Cl, according to reaction 6. With KCl present in the deposit, reactions 2 — 5 are also plausible to occur in the K 2 SO 4 deposit. What strikes us as interesting is the fact that the Pb-species are enriched into a compact region within the deposit structure.

Kinnunen et al. Unfortunately, the proposed K 3 Pb 2 SO 4 3 Cl phase has not been fully identified and corroborated to exist. Therefore, there is no thermodynamic data available for K 3 Pb 2 SO 4 3 Cl to estimate its melting properties.

Therefore, the amount of Pb and Cl found in the deposit is significantly higher than in the corresponding experiments with SiO 2 and NaCl deposits.

The layers of K 2 PbCl 4 on the furnace-facing side of the original salt particles included also some Na, in the cation ratio of Na—K—Pb. K 2 PbCl 4 was observed on and within the original salt particles close to the steel surface and on the oxide layer. In addition, the deposit was observed to have sintered throughout. Closer to the steel, the particles were bridging, implying that small amounts of melt had been present during the experiment, which indicates that Pb species had been distributed throughout.

The particles in colder temperatures had a fairly homogeneous conglomerate microstructure. In higher temperatures, the conglomerate microstructure became more heterogeneous and at the same time the furnace-facing sides of the particles were observed to be enriched in NaCl. The NaCl enrichment is likely a result of the K 2 PbCl 4 formation see Figure 6 and subsequent reaction back to volatile species reactions 2 and 5 and vaporization of KCl, KPbCl 3 , and PbCl 2 , which results in the depletion of K at the top of the salt particles.

The measured corrosion layer thicknesses are summarized in Table 3. The corrosion layer thicknesses were measured from the SEM backscatter images. The thicknesses were measured in 10 separate points per sample along the oxide layer. Any gaps between oxide layers were not included into the thickness measurements. Table 3. The corrosion layer under the SiO 2 deposit was observed to be the thickest compared to other deposits with the same exposure time.

Interestingly the smallest amount of Pb and Cl was found within the SiO 2 deposit after 24 h exposure. The layer closest to the steel consisted mainly of Fe and Cl, indicating the presence of FeCl 2. In addition, minor amounts of Pb and Cl were observed within the layer.

The compact and intertwined morphology with PbCl 2 and Fe x O y implies that melt had been present at some point. The corrosion products were observed in layers consisting of Fe and O. The Fe x O y layers were mixed with minor amounts of Pb and Cl. The amount of Pb and Cl was observed to be higher close to the steel surface than in the outer part of the oxide layer Figure 8. Closest to the steel there was a layer consisting mainly of Fe and Cl, followed by layers with intertwined Fe, Pb, Cl, and O.

Na was not observed within the corrosion layer. In addition, there were several Fe x O y layers mixed with PbCl 2. The bulk of the PbCl 2 was found in the middle of the oxide layer, in droplet-like shapes Figure 9. Otherwise the oxide layer consisted of Fe, Pb, Cl, and O.

The Fe x O y layers were porous and PbCl 2 was observed on the furnace-facing side of those layers. The Pb-containing species were observed on and within the oxide layer.

This is similar to results reported by others. In addition, some signs of FeCl 2 formation at the steel surface were observed.

Contrary to the other experiments, FeCl 2 was not clearly observed at the steel surface. Even so, its presence cannot be completely ruled out. K, Pb, and Cl were observed within the oxide layer similar to the KCl deposits, and they were associated in ratios corresponding to the composition of K 2 PbCl 4.

In addition, analysis showed KCl present on the oxide layer. Pb was observed as K 2 PbCl 4 on top of the oxide layer. Within the oxide layer, some K 2 PbCl 4 was observed. In addition, within the deposit, Pb was observed in roughly a ratio with Cl and with some K present. It is also possible that it takes a long time for the PbCl 2 to reach the steel surface and the corrosion reaction initiation is delayed.

The SiO 2 deposit resulted in the thickest corrosion layer, followed by NaCl, which forms a melt together with PbCl 2 but does not react and form solid Na—Pb chlorides. The difference in oxide layer thickness between the corresponding SiO 2 and NaCl experiments is likely due to the fact that it takes a longer time for PbCl 2 to reach the steel surface when it can be bound in molten phase with NaCl. The formation of a PbCl 2 —NaCl melt lowers the partial pressure of PbCl 2 in the gas phase, which slows down the migration to the steel surface.

This is supported by the similar corrosion behavior, neglecting the thickness, between the deposits. With both deposit materials, the oxide layer was similar in nature and composition, suggesting that only the initiation was slower with the NaCl. With Na 2 SO 4 the corrosion layer was thinner than with NaCl although the oxide layer was qualitatively similar.

The formation of Na 3 Pb 2 SO 4 3 Cl further binds the Pb into a less corrosive compound, which inhibits the corrosion. In experiments with the K-salts, the reactions of PbCl 2 with the deposit material seemed to further inhibit the corrosion.

The KCl—NaCl mixture resulted in the lowest amount of corrosion. The formation of K 2 PbCl 4 inhibits the transport of Pb-containing species to the steel. In addition, the KCl is bound into a matrix together with NaCl, which means that even some of the resulting K 2 PbCl 4 is bound to a matrix, which inhibits the revaporization. The higher corrosivity of PbCl 2 is possibly connected to the active oxidation mechanism induced by Cl 2 or HCl. The oxidization of metal chlorides yields metal oxides and Cl 2.

The regenerated Cl 2 is again available for penetration of the newly formed oxide scale and to continue the attack on the steel surface.

In addition, the penetration of Cl 2 has been speculated to be enhanced by temperature gradients. An alternative Cl induced corrosion mechanism has been proposed for steel exposed to KCl. Both of the fore described corrosion mechanisms lead to the formation of metal chlorides at the steel-oxide interface.

The presence of FeCl 2 can further result in the formation of melt together with other corrosion layer or deposit components, resulting in rapid molten phase induced corrosion. In addition, in the both proposed mechanisms Cl is the key component, which induces rapid corrosion. In addition, alkali chlorides are also more stable than PbCl 2 , meaning they do not release Cl for the corrosion reaction as easily.

The liquid phase is in contact with the steel surface can also enhance the corrosion rate of the steel. The temperature gradient across both the deposit and the oxide layer enables melt formation in the higher temperatures.

The formed melt can trickle down to the steel surface and get in contact with the steel before it solidifies. In addition, there are slight temperature fluctuations that can cause an occasional rise in the steel temperature.

Table 4. When a binary melt of PbCl 2 —FeCl 2 is formed, the components are mixed. When O 2 concentration increases and FeCl 2 is oxidized to iron oxide, the mixture solidifies, resulting in a solid matrix of iron oxide and PbCl 2 observed in Figure 7. Due to the temperature gradient, the solid PbCl 2 is exposed to a driving force toward the colder temperature, i.

Vaporization from the iron oxide matrix and condensation at the colder surface is likely responsible for the PbCl 2 rich areas within the oxide layers as well as the porous iron oxide matrixes observed in Figures 8 — Comparison to Collected Boiler Deposit. The structure and chemical composition of the synthetic deposits were compared to a superheater deposit collected from recycled wood fired CFB-boiler.

The lower part tube side of the superheater deposit has a dense and layered structure whereas the upper part flue gas side is coarser. The structure and the chemical composition of the boiler deposit correlate well with the synthetic deposits used and formed in the gradient furnace.

As observed within the gradient furnace experiments and confirmed with the superheater deposit, K reacts with Pb and Cl and forms a K—Pb—Cl mixture even if Na would be available.

In this study, K—Pb—Cl was noticed to be highly corrosive, even though PbCl 2 seemed to be the most corrosive salt. However, PbCl 2 was not found from the analyzed boiler deposit nor from the gradient furnace deposits when K-salts were present in the deposit. The major Pb-containing mixture in both cases was K 2 PbCl 4. Although other ash forming elements e. This indicates that the mechanisms observed in the laboratory experiments are also relevant in more complicated industrial systems.

The chlorides, bromides, and iodides of all metals except lead, silver, and mercury I are soluble in water. HgI2 is insoluble in water. PbCl4 decomposes to give PbCl2 and chlorine at room temperature. PbCl2 : A white solid which doesn't seem to dissolve in cold water although a little will , but dissolves in hot water to give a colourless solution. Answer and Explanation: However, the two polar bonds of CS2 C S 2 are arranged in a linear geometry, the bond dipoles get canceled out and the molecule is non- polar.

Answer: Lead II chloride PbCl2 is an inorganic compound which is a white solid under ambient conditions. Is PbCl2 a precipitate? Is PbCl2 a solution? PbCl2 is an insoluble salt in water, so the solution will have two differents phases, the water and the lead chloride. To be a homogenous mixture, it should have only one phase. Does PbCl2 dissolve in HCl? Is AgCl soluble in water? Many ionic solids, such as silver chloride AgCl do not dissolve in water. Does lead chloride form a precipitate?

Lead II chloride can be made as a white precipitate by adding a solution containing chloride ions to lead II nitrate solution. You could use things like sodium chloride solution to provide the chloride ions, but it is usually easier just to add some dilute hydrochloric acid. Does PbCl2 solubility change with pH? Lead II chloride is essentially ionic in character. This is the oxidation state of carbon and silicon in CCl 4 and SiCl 4. These compounds have no tendency to break down into dichlorides.

Lead IV chloride decomposes at room temperature to form the more stable lead II chloride and chlorine gas. Carbon tetrachloride has no reaction with water. When added to water, it forms a separate layer underneath the layer of water. If a water molecule were to react with carbon tetrachloride, the oxygen atom in the water molecule would need to attach itself to the carbon atom via the oxygen's lone pair.

A chlorine atom would be displaced the process. There are two problems with this idea. First, chlorine atoms are so bulky and the carbon atom so small that the oxygen atom is sterically hindered from attacking the carbon atom. Even if this were possible, there would be considerable cluttering around that carbon atom before the chlorine atom breaks away completely, causing a lot of repulsion between the various lone pairs on all the atoms surrounding the carbon, as shown below:.

This repulsion makes the transition state very unstable. An unstable transition state indicates a high activation energy for the reaction.